What are they huddling on this indicator?!

Tank is otherwise healthy. I had 5 adult + two baby shrimps before I introduced 11 more two days ago. There’s enough algae and food for everyone in the tank but I found that after introducing the new 11 shrimps they started huddling on the Seachem indicator which is very odd… Only a few on the indicator are munching on the algae that may have developed on the indicator but the rest are more idle than moving… is this a concern? If so what do you suggest me doing? I hope they’re not stuck…