The server saves the potion effect amplifier on an int variable, but the packet sent to the client is byte, with potions with the amplifier over 127 the client will receive the wrong value, altho it isn't shown on the GUI, that is an inconsistency
and an issue when creating modifications
Comments 7
Although the two issues are certainly related, I don't think merging them makes much sense, as the NBT save format does not necessarily match the packet format, and one can be fixed without the other being fixed as well.
Relates to MC-118857 (not exactly a duplicate)