In new zabbix 5.0b2 classic graphs now show continuous line with connected dots when data is absent.
1. metrics interval is 1 min
2. metered host is disconnected for some time
3. the host is returned and the metrics gathering is resumed.
4. In classic graphs we see that the region with missing metrics is continuous lines now (connected dots). See screenshots for illustration.
This behavior is unexpected. Previous behavior of zabbix was - no lines at all in area where data is absent.