I feel like I also encountered this but I wasn't sure? It only happened sometimes for me.
I’ll try to investigate the cause of this bug, thanks for pointing it out! Do you remember exactly what icons you were selecting when the Dps wasn’t stacking?
unfortunately I don't remember. The best I can do without going back in is that if I had multiple types of DPC upgrades and upgraded one, it somerimes wouldn't change the damage until I bought more upgrades from a different item.
I have the bug too, it's manifested in different ways?
First it worked like this: when I equipped one ally and then another, it would completely ignore the second's DPS and just keep the first's. If I then unequipped the first ally, the DPS would drop to zero. https://www.youtube.com/watch?v=pueTHb7dQQo
And now it works like this: when I equipped one ally and then another, the second's DPS would overwrite the first's. If I then unequipped the second ally, the first's DPS would come back. https://www.youtube.com/watch?v=WpSK8_5IQc0
I'm not 100% sure what I did that made it switch, it's possible it was buying/equipping the next item but I didn't do before/after tests.