Comment 26 for bug 1792580

Can you see if the fix in mainline was also cc'd to 4.15 stable? That latest kernel is available from:
http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.15.18/

If 4.15.18 still exhibits the bug, we can perform a "Reverse" bisect to identify the commit that fixes the bug in 4.19