Throughput critically decreases without causing view_change

1*Steps to Reproduce:*
1) Prepare pool with 25 nodes
2) run load test from 3 instances:

python3.5 perf_processes.py -g pool_transactions_genesis -m t -n 1 -c 200 -l 10.00000 -y one -k nym

Expected Results:
Pool handles about 18 txns/sec or more. View change happens if needed

Actual Results:
Throughput slows down to 0. View change hasn't happen

Additional Info:

Possibly caused by fix from INDY-1642
Logs (+metrics + other stats) are available here: logProcessor:~/logs/throughput_decreasing