Trouble with Lights on Dimmer? (New To Vista)

We recently purchased vista for our Church lighting and we are having an issue with our house lights that our on a dimmer…They will at random times go from the desired % shoot all the way up to 100% then back down in a matter of about 1 sec…Is there a way to fix this issue…the company that installed couldn’t figure it out and we where not having this problem with our last lighting software (ETC that I hate)…any ideas?