My 3 signal has gone rubbish, the mast i usually connect to has vanished, well not connecting!
Not staying with 3 if this is permanent , getting about 2mbs now, 3G and 4G.
It's the same for me.
I think the problem is that they are reconfiguring for the rollout of 5G.
Some of that has taken some 3G and 4G cells offline, some of it is that they are trying to clear the 3G frequencies for 5G, so moving more traffic to 4G (if you have the misfortune to be in a "Supervoice" area, your 4G will be slower).
In addition, if they are removing good Huawei kit and putting in inferior Nokia and Ericsson kit, that won't help.
I've had to give up on Band 3 and stick to Band 20, which has limited bandwidth on my local Three cells, but seems less overloaded.
Band 3 has hopeless download speeds, but excellent upload.
Band 20 is just about good enough both ways, with much better latency. Of course, that's just on the cell I use!
In February, when the troubles started, the network routing was all over the place. Lots of failed connections. They seemed to fix that in a few weeks (not sure when, because I was away when they sorted it).
The lockdown has probably put paid to expectations of an early resolution of all the issues.
I'm hoping that when they have finally finished the changes, things will get significantly better. Of course, I don't have a 5G router, so that'll be another expense.
I've tried EE because they used to be far better (if more expensive). They were even worse than Three (EE used to use the same tower that vanished form Three - it's also vanished from EE)..
I've tried Vodafone. They are a bit better than Three, but at almost twice the price, and no publicly-accessible IP address. An A&A VPN failed to get round that - I'm not sure why.