I got following from google support
"Thanks for getting back to me. As I dig deeper into this, I was able to find some internal documented information. I’ll be sharing with you what I found.
There is a bandwidth limitation per viewer and per owner, and a limitation on the number of times a document can be viewed. The limits are 10TB/day and 50,000 views/day with bursts up to 900/min (15 QPS) per document. I believe this might be the drive back end limit you are reaching. Also, in June 2017 a quota for creating blobs of 100Gb/day was established. It’s possible to create files of bigger size, but after this quota is exceeded all subsequent blob creation operations will fail.
That is all the information I was able to get and I hope it is useful. If you have any other question around your G Suite account, please reply to this message and I will be happy to follow up with you. In the meantime, the case will continue to remain open."
I am monitoring drive usage in admin console. In three days i have uploaded 2275,55 GB ~ 758,5 GB per day. It really looks like 750 GB plus active uploads when the limit is reached,