I had a look at and it appears to have gone into both 5.3 (final) and 5.2.15.
For what it's worth, it took only a day or so to exhibit the issue on our (admittedly active) nginx/postgres/PHP server; we weren't doing any unusual work during that time. If you're using btrfs, and you can't apply a patch to the backports kernel, it'd be a good idea to revert to a 4.19 kernel for the time being.
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Laurence "GreenReaper" Parry