Try running the same calculation with 11.8.b1. I'm quite certain the reason is you have run out of memory, but in 11.8 we have optimized the memory usage of the multigrid method, and I hope it will work better. You can use 11.8.b1 with your 11.2 license, while for the official release of 11.8 you will need to have the 11.8 (or higher) feature in the license file.