UBC memory run out usually happen when compiling any software packages, sometime software bug or, some software require huge amount of memory (more than your VPS is allocated). If memory is run out, you may not even reboot as root from VPS. Usually host administrator has to reset the setting in this case.
If you found your VPS performance is acting abnormal (degraded due to over committed the allocated-memory or resources), do check your UBC parameters by
If any of error count column having more than zero, please do save your current work and perform