Extremely Unstable USB Drive Write speed (large files, exFAT)

hello, I've got a new 64GB USB Flash Drive and formatted it to exFAT, and never used it before.

while copying any files on this drive, (even large files, like videos or else) The write speed keeps going high and low. On task manager, the usage graph is 100% all time, Active Time is 100%, but Write speed reaches 0 KB/s, then raises to normal speed (20 MB/s) and shortly, goes back to 0. this also happens to response time, in range of 0 ms and 2000 ms.

help please. thx

**Update: Read speed is just normal and operational**