This is a known issue with the ZWO ASI294 especially when used with a very narrowband filter. Take a look at this post from Cuiv The Lazy Geek in CN.
https://www.cloudynights.com/topic/6...-nb/?p=9374592
You can basically see that pattern on the sensor itself (when you use the L-Extreme filter) :-
https://www.cloudynights.com/uploads...1558261608.jpg