This is resolved with Dell OpenManage Server Administrator 9.3.1. See the workaround section if you are unable to upgrade.
For the latest details on a new version of OpenManage Server Administrator that supports ESXi 6.7 U2 and later, see this Dell EMC KB article:
OMSA: Hosts with ESXi 6.7 Update 3 become unresponsive to vCenter with task time-outs if OMSA 9.3.0 installedWorkaround:
To work around this issue, remove the unsupported “Dell OpenManage Server Administrator 9.3.0” VIB.
- Open an SSH connection to the host, see Using ESXi Shell in ESXi 5.x and 6.x.
- Log in as the root user.
- Use this esxcli command to uninstall the Dell_bootbank_OpenManage_9.3.0.ESXi670-3465 VIB from ESXi 6.7 U3 host:
esxcli software vib remove --vibname=OpenManage