Certain IPMI modules (SuperMicro X10-based) return non-present sensors, but error out on data retrieval. Because got_thresh_reading(...) in src/zabbix_server/poller/checks_ipmi.c handles any errors as network failures this leads to other sensors from the same machine to silently fail as if real network failure occurred. I'm attaching patch that treats the "non-present sensor" error as "not supported". The difference before/after the patch is clearly seen in the attached chart.