I specifically remember I was trying EE out for MBB and also used a Samsung S10e at the time and noticed overnight the mast had been pushed some change's (noteably the PCI - Physical Cell ID) changes on pretty much all masts in my area and beyond.
Then I noticed reduced speeds (200's become 100's "mbps") and this never really changed and record figures I had acheived before have since been unreachable (at least for 4G but then 5G isn't exactly on par with others either)
It's almost like traffic management or QOS was imposed on the network
I even tested the network during the 1st proper lockdown when the cities where deserted, and couldn't realy push the network to its potential, a spot in London gave me 400+mbps previously but the change on the network rendered that impossible to acheive again,
Birmingham city centre nothing really changed from when it was full of commuters and shoppers to when it was deserted and littered with the odd sneakey copper.