Possible Defective Humidity Probe

I believe we may have an issue with our humidity probe. It is randomly spiking from 50-58% RH to 90+ in a matter of minutes although the temperature of the room is pretty constant, it's also fluctuating there, just not as bad. Seems to me that shouldn't be possible as the RH can't fluctuate that quickly in a small room that is kept at about 65 degrees that has no air coming in from the outside, the air chillers just recycle the air inside. Please advise. Thank you.

Did you check it with another sensor? Some airconditioning units in fact do humidify or remove humidity. Some units do this only for a limited time depending on the water reservoirs they have.

I only have the one from you guys, I will have to look into getting another one and comparing the results.

Maybe you have one from a home weather station. Just to compare when it is high as you think

another way to test it is to put it outdoors - in a covered area (so not in the rain).

We put the sensor outdoors, according to the current weather in this general area, it's 81 degrees and a relative humidity of 51%. After about 5 minutes outside, the probe reported back about 83 degrees, which I anticipated a few degrees of fluctuation, the humidity still kept bouncing around a lot between 68% and 54% within just a 10 or 20 seconds. Does that seem normal?

yes that could be accurate depending on airflow going into the unit. watch it out for a spike to 90% like you indicated

Unfortunately I couldn't leave it outside for an extended period of time, because of security reasons. So we've brought it back in. I have ordered an indoor humidity sensor to use to compare the results and see if it is indeed an issue with the humidity sensor, or an issue with our air cooling systems. I will keep you posted.