Fidel YIN

However, this can also be reproduced on my laptop with AMD R7 M360 GPU and my desktop with AMD RX580 GPU. I don't think it is an issue relating to specific graphics.

can confirm in 1.14.4, 1.15.2 and 1.17.1

This is the result of profiling when chat lag and prompt lag occur.

Chat lag

Prompt lag

Looking the ticktime and CPU usage, when lag occurs, the ticktime is very high, but the CPU usage is relatively low. Therefore, I think a thread blocking may have occurred.

Chat lag: Tick 249:

[00] scheduledExecutables(1/1) - 98.28%/98.28%

[01] |   unspecified(1/1) - 100.00%/98.28%

[01] |   fabricClientEntityUnload(1/1) - 0.00%/0.00%

[00] updateDisplay(1/1) - 0.85%/0.85%

…

Prompt lag: Tick 70:

[00] updateDisplay(1/1) - 97.73%/97.73%

[01] |   unspecified(1/1) - 99.98%/97.71%

[01] |   mouse(556/556) - 0.02%/0.02%

[00] unspecified(1/1) - 0.96%/0.96%

[00] gameRenderer(1/1) - 0.74%/0.74%

…

When lag occurs, unspecified categories under scheduledExecutables and updateDisplay take up most of ticktime.

It happens not only in chat, but also in displaying prompt texts when toggling mod functions (eg. tweakeroo, minihud, etc.), so it may be caused by text generation and rendering.

Besides, it is worth mentioning that the lag is even worse when Fabric is installed.

This still happens in 1.17.1.