When installing a new version of Sharegate with the MSI installer, the installation is cancelled and the application is not updated on the next launch.
This problem usually occurs if you try to update Sharegate but select a different installation mode than the one used in the last installation, for instance if you tried to install the new version for "Only my user" over the current version that is installed for "All Users". We do this in order to avoid having two different installations on the system which could be confusing for the end user.
While Sharegate includes an auto-update feature that will prompt you if there is a new version of the application available, some users operating behind a firewall or in a network that doesn't have access to internet may have to use an installer that was downloaded from the Sharegate website. If it is the case, it is important to ask your system administrator to uninstall any previous version of Sharegate to avoid any conflicts while installing a new version of the tool.