I have two Humax HDR-FOX T2 boxes identically configured with same channels deleted and identical favourite channels. If I choose guide, find, genre, movies on each box I get a different list of 400 movies displayed. I wondered why this was the case out of curiosity..
This has come up before.
In 2014 I gave up after 2 years of trying to notice a pattern to what was found out of the 400+ it could have chosen for the 400 limit.
I suspect that it is a knock on effect of the harvesting of the epg from the broadcast resulting in the physical storage being of a different sequence and the epg query of those events not being fully indexed sort wise, and then only sorted after the 400 limit is reached.
For a full result list there is the webif epg search.
Another frequent quirk of when there are a lot of "Movie" results is if you sort them using the blue button into A-Z sequence the sorted results first include about 320 of those results sorted A-Z then this is followed by the other 80 after that sorted in to a smaller list that goes from A-Z. This quirk doesn't happen every time but once it does happen it continues like that for at least a few days.
I've also seen something similar on some of the other Genre results. E.g. When retried it just now for 'Education'. There were 150 results split into two A-Z lists of 126 results followed by a separately sorted list of 24 results.