WT restarts the transaction ids upon restart. To reset the stale transaction ids written to the data files, the checkpoint write generation numbers are compared against the last connection base write generation number. Upon successful recovery, a checkpoint is triggered to ensure the stable data is written to the disk.
The recovery checkpoint doesn't include the latest base write generation number used for ongoing operations. It has only the base write generation number calculated at the start of the recovery. Due to this if the server gets restarted again without any further checkpoints, any transaction ids that are written with write generation number between the recovery start to recovery end can lead to data corruption.