Tension to loose and missing stitches

It appears that there are two issues: skipping stitches, and, loose stitches. Let's deal with them individually but first some general points to check.
1. Change both needles for completely fresh ones out of the package. Make sure that they are inserted all the way up, this is very important. The right needle should appear longer than the left one. Make sure also that you are using the correct needles for your serger.
2. Use a good quality thread with very little stretch, almost no fuzzies, and in pastel colour. Dark thread ages quicker, therefore has a shorter shelf live. A good quality sewing machine thread is also acceptable.
3. Make sure that the tension dials are clean and free of lint or other debris.
4. Re-thread the serger in this order, keeping the presser foot in the down position at all times
a) Upper looper. Ensure that the thread is securely embedded inside the tension discs. Place the thread tail under the presser foot to 11:00 o'clock and place the presser foot down again
b) Lower looper. This is the difficult one to thread but make sure that all the thread guides are properly threaded as well as the upper looper elbow. Check that the thread is lodged between the tension discs. Once the lower looper eye is threaded, place the thread in front and over the upper looper and then under the presser foot to 11:00 o'clock and place the presser foot down again.
c) Right Needle. Thread the right needle path, again ensuring that the thread is between the tension discs. Place the thread tail under the presser foot to 11:00 o'clock and lower the presser foot.
d) Left Needle. Proceed as with left needle.
e) Double check that all tension dials have their respective threads embedded between the discs by pulling firmly up on each thread above the tension dials.
f) Check that the stitch length is set to between 2.5 and 3.0, differential to normal, blade position to middle, blade is engaged, and upper looper converter not in use.
g) Set tensions to recommended setting for 4-thread overlock.
g) Make a test stitch out. How is it? Still having the same issue/s?
If yes, continue with the items listed below, otherwise have a great time serging.

Skipping Stitches:
1. Check that the looper tips are smooth. Burrs will cause problems.
2. Check that the needles match the type of fabric being sewn.

Loose Stitches:
1. Double check threading.
2. Debris caught between tension discs will also manifest itself in loose stitches. Take an 8" X 6" piece of medium weight clean and lint free cotton fabric, fold it in half length-wise and pass the fold only firmly between the tension discs from top to bottom (with the presser foot up and no thread in the tension dials).

Re-thread and test stitch. How is it now?

Skipped stitches
1. The needle is not inserted correctly
Remove needle & reinsert needle( flat side towards the back of machine)
2. The needle is damaged
replace with new needle
3. The wrong size needle is being used
Choose a needle to suit the thread & fabric
4. The foot not attached correctly
Check & attach correctly
5. If the above suggestions don't help then the machine needs to be checked
For a timing problem,, the feeddogs may need to be checked to see why they are not moving the fabric thru the machine.

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Skipped stitches

1. The needle is not inserted correctly

Remove needle & reinsert needle( flat side towards the back of machine)

2. The needle is damaged

replace with new needle

3. The wrong size needle is being used

Choose a needle to suit the thread & fabric

4. The foot not attached correctly

Check & attach correctly

it's also possible that the machine could be slightly out of time

try adjusting the top thread tension one number or letter higher at
a time till the stitches look correct
change the needle
Correct needle insertion is mandatory for proper use of your sewing machine.
Raise the needle bar to the highest point, then loosen the needle clamp screw to remove the old needle.
Place the new needle in the needle clamp with the flat side of the needle facing the back, (round needle, the groove in the needle should face away from the shaft).
Push the needle all the way up as far as it will go. Then tighten the needle clamp screw.
also check the bobbin to see if it's warped

it's very possible that the machine is slightly out of time & needs to be service at a sewing machine shop
is the fabric & thread & needle compatable with each other?
did you use every thread guide when threading the machine?
is the bobbin in correctly?
is the bobbin warped?

It is very possible that the timing is off, which often occurs with broken needles. A common symptom is that the needle will not pick up the bobbin thread. Missed stitches aren't necessarily timing related--be sure to install brand needles often and use the correct needle for the fabric & thread you are using. Using the wrong needle will often cause skipped stitches.

What to Do If Your Sewing Machine Is Skipping Stitches

10 reasons for skipped stitches

Here What to Do if Your Sewing Machine is Skipping Stitches

Basic Maintenance Tension Skipped Stitches

You can search for sewing machine timing or take it for service.

try setting the top tension to 4 or 5 & see if the machine sews any better, you should see a nob or dial with numbers or alphetbet letters on it, that's normally on the left side of the machine
also try changing the needle, it's possible that it's bent or blunt
also clean under the needle plate & in the bobbin area for loose threads & lint

have you tried changing the needle
try rethreading the machine top & bottom
also clean under needle plate area & bobbin area for loose threads & lint

the name & model are not told in the question

try a tension of 3 or 4 maybe even 5 but I wouldn't go any higher than that

put in a new needle

clean under the needle plate & in the bobbin area for lint or loose thread

it is also possible that the tension dial is gone bad
& it would need to be serviced

The left needle thread tension is the problem if the seam can be pulled open. Check the threading and tension on this needle, you may find that the stitch looks okay on the top but on the underside the left needle thread is actually lying against the right needle stitching.

Check the left needle tension device is working, clean it according to the manual instructions, rethread and ensure it is set to the normal number (probably 5), then test again and see if its still happening. If so the tension device is probably faulting and will need a service.

Reading your description again, if the whole seam is pulling apart fully, then all the tensions are too loose. Either way, I'd take it to the Husqvarna dealer for a service, all machines benefit from one at least every 2 years.