This occurred yesterday and we did the updates in December.
The transactions with missing links are from AP Invoice Posting as well as from the Invoice module.

The description in the release notes to seem to be related to my issue.

I will be manually reviewing all retrieved batches to ensure the links all appear. It's a whole lot easier to add them before posting than afterwards! Maybe I'll find a pattern for those that are missing links. It hasn't happened often so is difficult to troubleshoot.
Thanks
Karin