Terrible performance with large forest fires

I'm afraid this is not a bug, this is lag due to a lot of fire needing to be processed on your PC, just like igniting a ton of TNT at the same time.

I can confirm this for 1.14-pre1, and 1.13.2 as well - 1.12.2 performs much smoother when there is a large fire. Added two screenshots, one on 1.14-pre1 on a Buffet Dark Forest set on fire, the other one 1.12.2 with a customised Dark Forest only world set on fire, With the F3-Shift screen turned on, going down to the thing that seems to cause the most lag (root.gameRenderer.level.terrain_setup.rebuildNear).
Edit: I do realise that my 1.14 is running on Java 12 (running quite well actually) - I also tested it on the bundled Java with the same result.

Still in all 1.14 Pre-Releases

Still in 1.14 Release

It was easier to have a tree lit on fire and have the game run smoothly pre-1.14. Now it lags too much.

Can confirm in 1.17.1. Doesn't even need to be a large forest; a few burning trees are enough to cause frame rate issues.

That's worse in 21w39a

Can confirm in 21w40a.

This issue was fixed, but keeps being reopened. The amount of lag has been reduced by a drastic amount to when this was first introduced. This one must stay closed.

I have created a new ticket for the post-19w45a issue: MC-240450.