My colleagues have also experienced this issue. It appears that if Qspice remains inactive for a period of time, it automatically uninstalls during its execution. Instead of prompting for an update, a pop-up for uninstallation appears. (it seems not related to internet connect, but if inactive for a period, the option is uninstall instead of update).
Jeff did mention about a timer in Qspice.
Qspice Installation - QSPICE - Qorvo Tech Forum
Mike mentioned offline installer is in their plan.
Offline installer for QSPICE - QSPICE - Qorvo Tech Forum
Considering that Qspice is undergoing frequent changes, there is a valid concern regarding people reporting issues from using outdated versions. Given the workload of the developers, it is indeed true that Qspice should enforce updates to prevent such problems.