Nodes are dying with OOM errors 

Nodes are dying with OutOfMemory exceptions on Linux platforms.

The DataStax Enterprise Help Center also provides troubleshooting information.

Nodes are dying with OutOfMemory exceptions.

Check for these typical causes:

Row cache is too large, or is caching large rows
Row cache is generally a high-end optimization. Try disabling it and see if the OOM problems continue.
There is a large user query running on the node which takes up all the heap
In production, understand and test all queries upfront to avoid arbitrary query patterns. Test to discover each query's max response size. Paging in CQL can often prevent a query from pulling too much data at once.

If none of these apply to your situation, try loading the heap dump in MAT and see which class is consuming the bulk of the heap for clues.