Comment 52 for bug 1796292

... and, just in case, I've uploaded also a test kernel based on the latest bionic's master-next + a bunch of extra bcache fixes:
https://kernel.ubuntu.com/~arighi/LP-1796292/4.15.0-55.60+lp1796292+1/

If the previous kernel is still buggy it'd be nice to try also this one.