EFS Burst Credit

Since a few days we observe a strange behavior regarding the burst credits on one of our EFS Systems. The credits are going down: and the percent IO Limit does corresponde to this behavior: But checking the write, read and total IO bytes, there are no significant changes:

I am also not aware of any changes on the 3 EC2 systems accessing the EFS causing this issue.

Do I read these metrics wrong. Any hint to find out and understand what is causing the burst credit usage is very appreciate.

Thanks in advanced.

Andi