When running various redstone contraptions... some examples including...

Ilmango's 2x2 Spruce Tree Farm,

Ilmango's Fast TNT Efficient Basalt Farm 

Kdender's Self Sustainable Fungus Tree Farm

...there is considerable game breaking lag and sometimes locking up completely. In the case of the tree farms mentioned above I have noticed that performance drops to under 10fps, I have tried on other machines so I know the issue is client side. I have had to force-close Minecraft in some instances, especially when testing the Basalt farm.

This leads me to assume that this is probably caused by redstone light update changes that were not happening in earlier snapshots of 1.16, would be great if this was resolved for 1.16.2. 

I tried to find this on the bug tracker but as I couldn't I thought I would report it anyway. I