test/format does not currently configure LSM with timestamps or prepare, by default, with a note that it's waiting for WT-4067 to close. WT-4067 has been resolved, we should allow LSM to test with timestamps.
WT-4162Re-enable test/format LSM testing with timestamps
is caused by
WT-4067Enhance LSM to not pin as much history in cache
WT-4093Temporarily disable test/format LSM and timestamp testing
WT-4226test/format LSM configurations can misconfigure prepare and timestamps