Not exactly an issue, but can be changed in the config. (also make sure Rayquaza knows Dragon Ascent)
You may experiance another issue where you can't use the z move. Just so you don't worry about it and have to wait for a response, below is the fix in case it happens:
By default, Mega/Z moves are used in the Ultra world as this is a gen 7 dimension, however, in all other worlds, dynamaxing is default. This may cause you to not be able to use mega or z-moves correctly.
There is a way to change this to make it so mega/z moves are the default thing, you do this by finding the "pixelmon.hocon" file in your config foldxer and editing the following setting (be sure to close your game first):
# Which dimensions use Gen 7 mechanics by default. Otherwise, they'll use Gen 8.
oldGenDimensions=[
72
Put a 0 under 72 (and put a comma after the 72).
72,
0
Once this is done, save the file and re-launch the game and Z moves should be working as intended.