Is there a sensitivity setting?

Is this a Fuji camera?
Check to make sure you have not set an aperture correction override. (Exposure compensation setting) Also check the metering mode or Exposure mode. You may also have the sensitivity set incorrectly. If this is the Fuji XT20 there are three exposure sensitivities setting it too high will cause this problem I expect.

adjust your sensitivity settings if you can. It may be getting shadows from birds...

Maybe they are being tripped by moths or other flying insects.

Check the settings that influence the exposure when your camera is in manual mode. There are three variables that you can adjust to change the exposure: ISO sensitivity, aperture (diaphragm) and shuttertime. When for instance the ISO is set to 100, aperture to F16 and shutterspeed to 1/1000 you will need a huge amount of light to get anything else than black pictures.
In a normal daylight situation you should get some results when using approximately the following settings: ISO100, F5.6 and 1/60 shutterspeed. Adjust these settings depending the light conditions and the results you get.

The d90 takes excellent pics, but you need to understand the settings. White balance determines the accuracy of the color by setting what the camera sees as whit compared to what you do. Then you need to set the ISO, which is how sensitive it is to light. The higher the number, the more sensitive. In super bright situations you may need to go as low as 200, 800 in lowlight. 400 is a good average, 100 is rarely used. then your aperature value (a/f) this determines how much light the camera actually lets in, not to be confused with the sensitivity (ISO) which is specifically how sensitive the film is (not that you have any). Then is the shutter speed, which is how long the camera exposes the film when you hit the button-for fast moving objects, you want the shutter to open and close really fast so it doesn't blur;if it stays open too long it will capture the object in motion-if someone is running and you have a slow speed, the image could be the runner taking three steps as opposed to a still picture. To start.your setting when you take a pic, look at how much light you have. For indoors with no lights on during the day or outside cloudy, ISO 400. In at night with bright lights or outside sunny day, ISO 800. Then determine the speed of your object. A good standard for slow objects is 1/20-1/60. Set that, then set your aperature (f value) so the picture looks at the right brightness. If you adjust the aperature all the way and still need more or less light, adjust the shutter. Then cycle through your white balance options to make sure your color looks right and take a picture. If it comes out really grainy, your light settings were not right, you should pay attention to your ISO and aperature settings.

These cameras were designed to be high sensitive to light. If the Flash is set for Auto Flash, the camera tends to use ISO 400 whether the flash is fired or not. This was done to increase the working range of the flash.
In order to change this setting please go into the Menu (Capture+ tab) and set the ISO for 64, 100 or 200 in order to reduce the graininess. However this will lead to slower shutter speeds in low light.

Yes, it's possible.
The flash sensor is calibrated for a 35mm optics & iso (asa).

You may have to "UP" your digital camera's iso sensitivity to 800 or so.

You will have to experiment with it at various settings.
Try using the "bracket" sewtting on the camera.
It takes three pictures when you press the shutter button; the three have different "values" of brightness.

The bracket setting is on the UP arrow, where you can choose "single frame", "continuous frame", bracket, etc.

Hope this helps!

Try putting it on the daytime setting.

Have you tried decreasing the sensitivity on the controller? On the main dashboard click options and it should come under "sensitivity". Try the lowest setting.