Ok, but clearly it hasnt always done this, since I imagine youve been using this plugin for a while. So something is different now compared to before. There must be some specific circumstances that trigger this error. Does it happen with ANY Pokemon with ANY move in its moveset? Or does it only happen with specific factors? Does it happen with Z-Moves, too? Have you tested if recompiling fixes the issue? Starting a new game? Are you testing this during normal gameplay, or in debug mode? Did you install any new plugins or change any code before the error started occurring? Did you check your PBS files to ensure that you didn't accidentally overwrite your Max Moves from your moves.txt?
This is what I mean by "context". You're just posting an error with no information and asking me to fix it, and I have no idea if you've done even the most basic troubleshooting yet to rule out potential possibilities, or what state your game is in, or what potentially triggered the error, or where to even start looking. Help me so I can help you.
Just from the error log though, it seems to be pointing to one of your moves in the Pokemon's moveset being unable to be converted into a Max Move. The only reasons I can come up with for why this would happen are:
A) You somehow found a way to Dynamax a Pokemon that should be impossible to Dynamax, such as a Shadow Pokemon.
B) You have a move in the Pokemon's moveset that for some reason is impossible to convert into any compatible Max Move. For example, a custom type that you added that you didn't create a Max Move for.
C) You have a plugin or some custom script installed that is overwriting how your game loads save data, and thus isn't retaining any of your Max Move data. I know of at least one plugin where this might be the case.