I am seeing this too, very frequently and intensely since 6.08, on an Intel iMac. 4.2 GHz quad core i7-7700k, 32 GB RAM, Radeon Pro 580 8 GB.

I tried replying to bug reports but I wasn't able to post there. This did not occur for me prior to 6.08 but I pretty much run into it every session now, if I play long enough (within an hour or two of starting).