High EFS EUC1-ETDataAccess-Bytes read costs but I can't see these reads on Cloudwatch

Hi there,

we see drastically increased EFS daily costs in one account. It increased from one day to the other (07.12.) from ~10$ per day to ~90$ per day (till today). If I further observe it, I can see that it's EUC1-ETDataAccess-Bytes - and the reads (found via Cost Explorer with this service as filter, grouped by api operation). What I absolutely cannot see is increased reads in this EFS filesystem via Cloudwatch... not at all. This filesystem has ~20GB in total size and we are talking about 1.8TB reads per day that get billed! There must be any metric I could check... but there isn't - in fact everything dropped! TotalIOBytes, DataReadIOBytes,MeteredIOBytes,MetaDataIOBytes .. everything dropped since 07.12.

Can somebody point me to things I could check?

Thx!