I dont use a managed host. So I dont know what kind of issues gportal is giving you. But the only reason you should ever see the client mod handler is if your modlist.txt isn’t configured to exactly match the load order running on the server, or if you’re not running the same mod version as the server.
That screen’s entire purpose is to prompt you that your client has not loaded with the exact same modlist setup as the server you’re trying to join and to give you options to rectify that (download the right mods and RESTART TO LOAD YOUR CLIENT WITH THE CORRECT MODS IN THE CORRECT ORDER)
If you have the right mods in the right order, you will never see that screen and you will never need your client to restart (because that would be entirely redundant) except for version mismatch
TL:DR you dont have the right configuration saved clientside, so the mod handler steps in to fix it for you and restarts your game with the right setup necessary to join with.