AFAIK, the 50Mb upload limit is a quirk of some SH2’s , effectively leaving the ‘factory’ with a 50Mb limit on the upload , leaving it connected for a while ( should you be getting 50Mb instead of 110 ) allows a firmware update to remove limit , (should the limit exist) , leaving the SH2 for a while isn’t anything to do with changing or updating your ‘profile’ , so if you are using a third party router that is compatible with the upload speed available, you should get the higher upload 110Mb upload immediately.
If service has been correctly set up ( and if your are getting 900Mb download, that seems likely , as the only profile with 110Mb upload is the 900Mb download profile) , the 72 hour wait is irrelevant, your third party router obviously won’t be getting a firmware update from ‘BT’ , but is this third party router capable or correctly set up ?
Post your own router stats , or connect to the ONT with a wired PC , set up a PPPoE session and run a speed test from the PC , that eliminates the router ( BT or your own ) completely, obviously you could leave the SH2 connected, hopefully its firmware is updated and it delivers 110Mb upload , proving the service is delivered as expected, if you do this and don’t get the firmware update automatically, it can be ‘pushed’ onto the device, but only after giving the ‘automated’ update a chance.
