I have same problem for six month and i want to compare with other people before i spend more money.
Accounts die between day 20 and day 35, almost all of them, very consistent. Not day 2, not day 90. Something happen around one month. I use residential rotating, one session per account, sticky for 30 minute.
My theory is the rotating is the problem — the account see a new city every session and after some week it add up. But mobile proxy is 8x the price and i not want to pay this for 60 account if the problem is something else.
So tell me what you run and how long your account live. Residential, isp, mobile, datacenter if you are brave. And say the number, not "they last fine".