I have run into an issue with E/M shops where I've gotten a message that said they have reached the limit on the number of projects that can be accepted. This was after I accepted around 15 to 20 at once. The pins remained on the map, and I was able to accept more after I completed some.
The limit message comes up for me when I look at one without claiming it, and then try to look at it again before the three minutes is up. I was just noticing there are a lot left on the board, and I'm thinking people may have been hitting a limit.