Campaigns can be "frozen" in 2 cases.
Autostop. The campaign is automatically stopped if the deviation of the actual CPA from the planned one exceeds 50%.
Decrease in the pace of an ad campaign. If the deviation of the actual CPA from the planned one is higher than 20%, but lower than 50%, the pace can decrease significantly, up to almost complete cessation.
What to do?
Check that the postback is working correctly.
Make sure that the target page is not blocked by antiviruses, Roskomnadzor or operators.
Analyze the breakdown by hours, track how LR (lead trade) changed, look for reasons for the decrease in LR, which led to a decrease in the campaign pace. If everything is in order for the first two points, your CPA rate is probably understated, and other advertisers offer higher ones. In this case, it is worth considering the possibility of increasing the rate.