Sandisk Extreme 64gb - very slow writing speed on MAC

I’ve bought Sandisk Extreme 64GB CZ80 from

After connecting it to my iMac, i’ve formatted it with HFS.

Now i have following problem - read speed are very fast (>200mb/s), but write speed are between 1-3mb/s.

I also tried to connect it to my macbook - write speed varies between 5-8mb/s.

How to solve this problem?

I wonder what the write speeds would have been if you hadn’t formated it.

I went from 177MB/sec write and 252MB/sec read to 28write/18read overnight. Also formatted for Mac (but they have been since purchase).

Reconditioning has no effect. Changing the format has no effect either. Any official way to recondition these things?