Exact same issue, after this week maintenance, I am unable to exchange any of the weekly items after today's reset. The gold exchange is possible, but that's it. I tried to change char, relog, swap server (normal), swap server (season).

One of my clan mate tried and it worked fine for him. 

Anyone managed to find the cause or somewhat solve the issue?

Yep, week 3 and still broken. Please fix this.

Even more infuriating, this bug isn't even listed in the "Known Bugs" report. How is this not known?

Don't sell your fish for gold bars. It fixes itself a few hours later. This also happens with other items like Arena of Solare tokens.

Just ran into this issue today. The exchanges I did last week didn't reset. Please fix this bug.

I forgot to post last week, but yep Week 5 and still an issue.

If you can't fix this system, then put the quests back on Fughar.

Week 6 still broken.

I'm pretty sure this happens, when you hand in the colcenaths in the window, between the game coming back up after patch and the next daily reset.

It counts for the new week, but the seal UI acts as if u did it the week before.

If you wait to hand in, until after the daily reset, you shouldnt have any issues.

edit:  yeah still zero issues, doing the exchanges after the daily reset following patch time.

I'm not even able to do the hand in until 1 or 2 whole days AFTER reset. So it's definitely not an issue of doing it too early.