Zabbix Web Scenarios huge response time

[nanorobocop]

Hello,

Zabbix running in Docker on OS X.
Created web scenarios for service monitoring.
Usually they work fine.
But sometime graph shows that request processed in 1 Hour, which is impossible because Timeout = 15sec.
Screenshot:
Tried both 3.0 and 3.4 - problem reproduced.
Any ideas what's the root cause and how to fix it?

Thanks!

[jan.garaj]

Alpine? https://github.com/zabbix/zabbix-docker/issues/141