Much slow down of responses of s3select requests several times today

Hello!

Today I met a suddenly slow down of my s3 bucket several times. Sometimes it worked well, but at other time it's 100x slower than usual.
I didn't meet this before today, just now I tried again and it became normal.
But I'm not sure whether this large delay will occur again. Also wondering if there's any daily limit on the bucket that when exceeding it shows huge delays.
Fyi, I'm using c++ aws sdk to send s3select requests to s3.

Can anyone help me? My bucket is s3://pushdowndb
Thanks!