I have been working to reduce the amount of data that could be lost in the event of a crash. This amounts to more frequent log backups and log backups right up to the nighlty backup. I changed backup job schedules and failed to notice I had 2 databases doing log backups at exactly the same time. This worked fine until the nightly backup job in one of the databases started. The agent stalled both transaction log backup jobs until the nightly full backup finished.
To fix this I just adjusted the schedule of one of the transaction log backups so the jobs were not at exactly the same time.