update not found for: 00000000000014372158, range: 17181384 an insert is likely more than ten percent behind reads Error: WT_NOTFOUND: item not found
I dug into the failure that came across with the ckpt-lsm configuration from Friday. Here is where the original error occurred. Note that there were many (> 100) of the "update not found" messages beforehand. The cursor.search error is the real one.

update not found for: 00000000000008750865, range: 17181455 an insert is likely more than ten percent behind reads Error: WT_NOTFOUND: item not found
update not found for: 00000000000000220284, range: 17181455 an insert is likely more than ten percent behind reads Error: WT_NOTFOUND: item not found
update not found for: 00000000000001304256, range: 17182459 an insert is likely more than ten percent behind reads Error: WT_NOTFOUND: item not found
file:test-000210.lsm, cursor.search: encountered an illegal file format or internal value
file:test-000210.lsm, cursor.search: the WiredTiger library cannot continue; the process must exit and restart
update failed for: 00000000000000141872, range: 19835621 Error: WT_PANIC: WiredTiger library panic

The failing WT_TEST home dir no longer exists on the AWS box.