This is an actual AntiXRay plugin for PocketMine-MP.
Unlike other so-called "AntiXRay" plugins, this one does not simply inform staff members if an ore is broken.
This plugin modifies the chunk packet sent to the client to make it look like a chunk contains a ridiculous amount of ores.
Added support for the full-release version of PocketMine-MP 5.0.0.
Removed support for older versions.
Bumped required PocketMine-MP version from 4.7.1 to 4.16.0.
Fixed incorrect items appearing in item frames (due to an obsolete workaround made in PocketMine-MP for 1.19.10).
Bumped required PocketMine-MP version from 4.7.0 to 4.7.1.
Removed a bug where plugins or virions sending fake blocks to the client, would trigger block updates by ActualAntiXRay making their efforts worthless.
This was the case with plugins using the InvMenu virion which would stop them from displaying block inventories to players.
This plugin works not because it identifies players who use XRay, but because it sends fake ore blocks to every player on the server whether they can see those fake blocks through XRay or not. Because of that, it is not possible to implement admin alerts in the scope of this plugin.
I understand that it is very frustrating if a plugin does no longer work and even crashes your server after updating. But simply posting "server crashed" does not help anyone.
Thanks to other users, the error was already identified and a fix can already be found on GitHub https://github.com/ColinHDev/ActualAntiXRay/releases/tag/v1.0.2 while the update is reviewed by someone from poggit.
But since you didn't provide any information, I only assume that this update fixed your error which came due to some protocol changes in 1.19.20. (So if you updated your server to support that version and after that, the crash happened, then your error should be resolved.) Next time, just head over to the plugin's GitHub page and post an issue along your crashdump! :D