Perhaps a memory leak (in the graphics driver, maybe) ?... But no log, no diagnostic...
Please, follow the
bug reporting rules.
As for memory warnings, if you ignore them, it is normal that the viewer ends up crashing. When you get one, you should log off as soon as possible and log back on. The warnings happen when the viewer failed to allocate a memory block (most other viewers would crash already at that point, but I added a lot of memory checks and fallback code paths in the Cool VL Viewer when it was still a 32 bits viewer, i.e. when virtual memory space fragmentation issues caused such allocation failures).
In any case, if it is only happening for the past two weeks, you should ask to yourself what you changed in your system two weeks ago... New driver version, perhaps ?
I very much doubt it is a viewer bug, but will wait for your logs before making my mind on it.