AttributeError: 'NoneType' object has no attribute 'request' during load

Steps to Reproduce:
1. Prepare new pool with 25 nodes
2. Run load test from 5 instances

python3 perf_processes.py -g pool_transactions_genesis -b 10 -r 2 -m t -c 100 -t 50 -n 3 -k "{\"nym\": 4, \"attrib\": 1, \"schema\": 1, \"cred_def\": 1}"

500 clients, 30 writes / sec

Actual results:
Pool stopped writing after only 11k txns (and less than 90 minutes) and cannot finish catchup

Additional info:
Logs will be available on LogProcessor:~/logs/attribute_error_11jul2018