Back in 19w13b, I was using firework rockets, and had some issues, but just brushed it off as lag. At some point later, I found that when the server lagged while I was using fireworks, it would bug the chunk, so any time I flew  in the chunk on an elytra, it would be giving me the firework effect endlessly, as along as it was inside the chunk. This effect did not happen for anyone else on the server.
Eventually upgraded to 19w14b and it continued, but recently we left our base and came back again later, only to lag and lock up (1 frame per every 10 seconds or so) when entering the area with the bugged firework chunks. Alongside the lag and locking up, getting teleported out of the area and waiting for the lag to clear allowed these messages to get printed to the clientside logs (The server does not lag any more than normal with this issue):

https://pastebin.com/mdgcgh65