when trying to claim boss rush rewards during reset The game displays "no more rewards can be claimed this week". However, no rewards were ever given.

I can confirm this happening to me and basically everyone else aswell

Yep, pretty annoying.  Apparently because they are making some changes to the rewards, but makes zero sense to delay this week's rewards for that; just implement the changes for next week's rewards!

According to "known issues" we should be able to claim them after maintenance 26th - deboreka up to duo inside as new addition. Don't remember anywhere mentioned this.

https://www.naeu.playblackdesert.com/News/Notice/Detail?groupContentNo=184

          "We've temporarily changed the Black Shrine Boss Blitz weekly rewards to be obtainable after the July 26 (Wed) maintenance.
          - With the July 26 (Wed) maintenance, some Black Shrine Boss Blitz weekly rewards will have up to DUO (II) Deboreka Earrings added to their reward table.
          - Thus, this temporary measure is to give adventurers who've cleared this week's Black Shrine Boss Blitz a chance to obtain the newly added rewards.
          * Please note that Black Shrine Boss Blitz weekly rewards will be obtainable as before after July 30 (Sun) 00:00."

Does that mean if you cannot claim the rewards that you got to wait to do the new boss blitzes? Because the allowances resetted. Or can you do them and you will later get the rewards from both weeks?

btw same problem like the others. No rewards given were given on sunday for the previous week.

As the post says, we can claim this week's rewards after WED maintenance, so it's just a few days' wait.

You can claim them from WED after maint to Sunday midnight. Later than that and they will be lost.

I saw the announcement on Saturday already, it's intentional and not bugged.