FVTT 13.351
DND5E 5.2.5
No modules
Legacy and Modern rules
The AE for Bless uses system.bonuses.abilities.save to add the 1d4 bonus, but this attribute does not add the bonus to Concentration saving throws. Tested with Akra from Starter Heroes.
system.bonuses.abilities.save should be made to apply to Concentration saving throws as well.
If system.bonuses.abilities.save does not apply to Concentration saving throws, that should be noted in the docs.
Edited to add: It looks like this may have been a transient issue on my end. Please close.