Current Build At Time Of This Report: 11.1.0.59347
Bug Information:
I had maxxed out (2) reputations today for Paragon Caches. Those being, The Undying Army (Shadowlands Reputation) and Council of Dornogal (The War Within Reputation).
Upon doing so, I went to the quartermaster as usual to claim my Paragon Cache that contains gold and other useful items. However, Upon going to them, They didn’t offer my a Paragon Cache and instead my reputation track reset to work on the next Paragon Cache.
I had this happen to me on 2 of my alts as well.
Happened with me today too. First with The Vizier, then again with Council of Dornogal.
[edit: Probably Hallowfall too]
oh so not just shadowlands
I had it happen with Hallowfall
Just happened to me with 7th Legion
they made a support article about it
#### Common Problems
* I maxed out my reputation bar with a faction and did cannot receive my paragon chest
* I didn't get any quest or chest for filling up my reputation.
* The vendor did not have any paragon chests or caches for me</em>
We have received several reports of this issue and can confirm it is not working as intended. Customer Support does not have a workaround or resolution that can be provided. We apologize for any inconvenience while our developers work as quickly as possible to resolve the issue.
I have missed out on three paragon caches from this bug already! I’m not even trying to max them out, just doing all the WQs for the extra 15undermine contract rep. Now i’ve missed out on FOUR paragon chests because a delve pushed me over.
The Bugs Within continues, another week, another paragon chest quest with no reward when turned in and completed - this week The Undying Army.
Fix your game as I’m getting sick and tired of wasting time traveling to the middle of no where to turn in what should have a reward box with decent gold and a chance at cosmetics I don’t have and getting nothing.
Just had this happen to me with The Wild Hunt (SL) rep. Had the flashing green checkmark, clicked on the NPC and then it reset my bar of rep. 
Super lame.
Happened to me with Flame’s Radiance. Hope there’s a fix soon.
Still bugged to hell (always Shadowlands rep for me, TWW seems to work and I have no idea with DF since the boxes are garbage I haven’t even tried to claim any rewards).
Sometimes I get the ? on the rep panel and on the map showing a paragon turn in location for a character, but they do not have a quest - talking to the NPC will make the ? go away and reset the bar in the reputation panel.
Sometimes I get a quest (and have the ? on rep panel) with no reward listed (so far this is always Paragon of the Undying Army), I can turn in the quest which will reset the rep bar, but receive no reward.
Multiple alts have gotten the achievement for obtaining a paragon box upon logging in or completing an activity awarding rep, sometimes getting just the ? on map, sometimes getting a quest (Undying), always without a reward.
Sometimes (actually rarely) I get an actual quest with a reward, turn in the quest, and get the reward.
Maybe it’s just a display / UI bug - but it is beyond annoying getting ? and quests with no rewards across multiple characters and not knowing whether I’m losing rewards or just having my time wasted.
Happened to me this week as well, with Dragonfall Expedition a couple days ago and Hallowfall Arathi today. I have an addon that notifies me when a paragon chest is ready for pickup, but when I went to get the chest, there was nothing available. My reputation bars did reset properly after achieving paragon, but I just didn’t get the reward.