Anyone who got the 'great news' text can probably expect problems.
I called up today and spoke to a lovely lady in Ireland who had full access to site information, and could confirm that most of Hatfield and a lot of Welwyn Garden City (both places where people got the text) are showing as red. Serious problems and lack of 4G intermittently as optimisation work is carried out.
The work being done, including to my local cell (which is on the roof of EE's HQ) is all to upgrade the capacity and 'optimise' the network. I suspect, although she couldn't confirm, that this is 4G+ upgrade work. My site is already 4G+ but the others around aren't, so I expect that eventually we'll have 300 or even 450Mbps service.
She said that there are normal 4G upgrades and 4GEE upgrades, the latter being the fastest speeds. She wasn't an expert and didn't understand when I talked about different carriers and if the should see what speeds/capacity each site had (maybe she couldn't see that level of detail) but it does explain the problems.
It's odd that it isn't showing on the EE checker for me, although some post codes do. Maybe EE can't quite predict the affected areas. I was told I shouldn't be getting 4G today as they're making changes, but I am - but maybe I'm on a more distant cell.
Anyway, the ETA for completion is Sunday 13th and she's going to call me back in the afternoon to check.
I recommend anyone having similar problems call 150 and ask to speak to someone in the network team. Anyone having problems might be very happy when it's all fixed! However, shouldn't EE be making it a bit clearer to the public what's going on? How many people will be saying 'enough is enough' and ditching EE as a result of problems that have been on and off for a few weeks?