Hi @mrforsythexeter and welcome to the Mattermost forums!
%appdata%\Mattermost is the path it should be, you can try to verify that by stopping your Mattermost application and then renaming the folder to Mattermost.bak f.ex. and start it again. If all your settings are lost, this is the right folder. Stop the application, remove the newly created Mattermost folder there and move the backup folder back (by renaming it to Mattermost again). If this experiment does not work and renaming the folder does not wipe your profile, we need to dig deeper. It could very well be, that your Mattermost application has been installed in some different folder or with in some kind of a security enclave with isolated directories, but I highly doubt that.
With regards to the keyboard shortcut you used: CTRL-Shift-r would have been the key combination for a full reset (including cache flush). You can also click this shortcut in the app’s menu:
