that is not a pmmp's problem, it could be anything caused that glitch/bug - A bug / some bugs in render dragon - A broken rtx texture pack (or a bugs in player rendering) - Related to the pink glitch on The Hive ?
I guess checking which packets are sent would help if it's server sided. Although, you would need an rtx machine, a relay(bedrock-protocol) to monitor the packets and a bds server which can easily be downloaded.
Using PacketLogger I got the list. Here's what happens when you turn on RTX: [2021-11-25 14:39:59:022] BatchPacket has been sent! [2021-11-25 14:40:03:803] BatchPacket has been received! [2021-11-25 14:40:03:803] RequestChunkRadiusPacket has been received! [2021-11-25 14:40:03:804] ChunkRadiusUpdatedPacket has been sent! [2021-11-25 14:40:03:804] BatchPacket has been sent! [2021-11-25 14:40:04:420] BatchPacket has been received! By the way, in Pocketmine 4.0.0 with RTX skins are displayed.