This seems to be caused by Focal's 5.4 kernel: after booting Ubuntu 19.10's linux-image-5.3.0-40-generic (5.3.0-40.32), which remained on the system after upgrading to 20.04, hibernate-disk (and resume afterwards) works fine.
This seems to be caused by Focal's 5.4 kernel: after booting Ubuntu 19.10's linux-image- 5.3.0-40- generic (5.3.0-40.32), which remained on the system after upgrading to 20.04, hibernate-disk (and resume afterwards) works fine.