It was 1.1.0 (factorio-data commit for future reference to removed logistic_slots_count
values for Buffer & Requester chests).
The changelog for 1.1.0 covered renaming the property, but it seems did not mention removing the limit for Buffer & Requester chests.
Thanks for pointing it out. I'll try to get a release out this weekend with the corrected behavior.
Edit: Easy code change. Just have to test it tomorrow.