Running current develop changeset 12997a276 on kodkod-aws I'm seeing test/format failures (4 out of 10) fail with:
[1582735577:312243][24084:0x7f3e4d8f2740], t, file:wt.wt, WT_SESSION.verify: __verify_ckptfrag_chk, 526: checkpoint ranges never verified: 2
[1582735577:312315][24084:0x7f3e4d8f2740], t, file:wt.wt, WT_SESSION.verify: __verify_filefrag_chk, 438: file ranges never verified: 2
The number of ranges varies between runs. This is a row-store only configuration.
There were recent other tickets that are all closed:
WT-5600, WT-5457, WT-5618.