Pre-allocated contact buffer is full, physics state is invalid.

I encountered several warnings each time I run the dm_control.locomotion example as below:
W0827 .544679 139749952841536 core.py:299] Pre-allocated contact buffer is full. Increase nconmax above 100. Time = 0.0000.
W0827 .545073 139749952841536 core.py:85] Pre-allocated contact buffer is full. Increase nconmax above 100. Time = 0.0000.
W0827 .546310 139749952841536 engine.py:323] Physics state is invalid. Warning(s) raised: mjWARN_CONTACTFULL
And then the episode will terminate with time lasts 0.5s only. Such time is not expected obviously. There were similar problems about this on github. I've read some of them and followed their instructions. However, I failed to follow the variable to find where it was settled or changed, both in code or all .xml files.
So, where can I increase that? Or anyway else can solve this problem?