I've read through about 5 pages of this and want to share my thought, hopefully I'm not repeating something on the following 8 pages.
I think there are lots of good problems being pointed out as the reason for the O's struggles. But I think it is a "moving" problem.
Is it Diggs is getting old/injured? Maybe, but he still had more than a step on the missed bomb yesterday, and had a key 11 yard catch late on 3rd and 8 against the Chargers.
Is it the O-line? Sometimes they are excellent and other times we have free rushers coming at Allen.
Allen off platform/too aggressive? Sometimes. But we seem to have a lot of untimely drops on perfectly thrown balls also that derail drives.
Is it the play calling? We've seen good and then some not as good. Time will tell if Joe Brady can zig to the defenses' zag, but it feels like we're in a better spot than with Dorsey.
I think some of this is also Josh/Brady not being ready for the rock/paper/scissors at times of the defensive play calls (hot routes available against blitz, don't get happy feet when there's a spy and no pressure but DO scramble when there's not a spy, etc.)
Then there are untimely penalties that derail drives, at times legit and at times seeming ticky tack/wrong (maybe that's my bills-colored glasses).
You put it all together and I still believe the offense is capable of putting it all together and looking unstoppable with the pieces we have (oh how I miss the days of our "no punt" streak), but there seems to always be something killing a drive, but that something shifts from drive to drive. If we just start executing with all 11 on each play things would look so much better. Are we missing practice time with Josh's injury/load management? Are we lacking a sense of urgency? Is the O coordinator change in mid-season causing growing pains?
TLDR: It's not one thing, it's a failure of all 11 to execute consistently.