I can confirm this is the problem I removed every single plugin tested / installed one by one does not matter what I do I still get error compiling it seems it's definitely in the Linux issue my host i use also thinks that's the reason.

One plugin (generally some of the minified, paid ones) tend to cause this issue with the compiler. It will not be fixed when they are unloaded during runtime, you'll need to remove them all and load them manually to find the culprit after a restart.

+1. Running into issues with Linux as well. 

Fallback handler could not load library /home/username/serverfiles/RustDedicated_Data/Mono/libKernel32
Fallback handler could not load library /home/username/serverfiles/RustDedicated_Data/Mono/libKernel32.so
Fallback handler could not load library /home/username/serverfiles/RustDedicated_Data/Mono/Kernel32
Fallback handler could not load library /home/username/serverfiles/RustDedicated_Data/Mono/libKernel32
Fallback handler could not load library /home/username/serverfiles/RustDedicated_Data/Mono/libKernel32.so
Fallback handler could not load library /home/username/serverfiles/RustDedicated_Data/Mono/libKernel32​

Those are not related to Oxide, also not issues.

Did some better log tailing, identified bad plugins post-update (in my case, BuildingGrades, PrefabSniffer, DynamicCupShare). All is well. Thanks @Wulf.

os : linux

15:46 [Error] Error while compiling:  error how to fix it ?

Merged post

fix it Cupboard plugins update fix it!