When Fairy Lights is used with FluidTank it will cause a crash when placing down a tank. It's reproducible and has been tested with only those two mods enabled. I've included a crashlog.
crash-2020-11-17_06.26.40-client.txt

It seems my mods failed to load mixin system. It's not compatibility issue.
Downgrade forge will avoid crash.

I'll continue to research this problem.

There's some tested info that the latest Forge version that doesn't crash is 35.0.15

Err, I am curious to why you mixin LazyOptional, that is incredibly invasive for something which seems like it should not be necessary.

I wanted to change the status(valid or invalid) of LazyOptional from inside of supplier.

Anyway I fixed the code not to depend on mixin codes. v16.0.8