next time the screen flickers go immediately to the even log and see if an error is recorded . If there is an error this may help shine a light on it . If there is no error code before jumping on the invertor you may want to test your battery . If your battery is getting old it may say 70 % but its may be failing . If the battery dies with less than two hours of use it may be time to replace the battery . bad batteries can cause a lot of different problems and if your not having any screen issues when its plugged in Id tend to look long and hard at the battery. If after replacing the battery you still have no joy then replace the invertor . This is a helpful video towards that end

https://www.youtube.com/watch?v=S87niyGJ...

Some other things to check are the screen cable at the hinges and the screen itself . Hope this helps