I think all the activity of moving offices etc is IRCC’s attempts to balance the work load and hit the deadlines. And pre-arrival services are a GOOD SIGN (I’ve signed up to some - some of them are quite in depth and funded - so they won’t give them to you unless you are an almost certain ‘yes’!)
Also, there is a big printing backlog at London, so they seem to be shoving some of the pure admin around a bit.
Also - to the person worried about change of address - the london office emailed me to confirm my address (and they’d put my house number after the street name - not usual uk notation) - they accepted a direct email response, acknowledged by email and the corrected address appeared on the letter the next day. Not saying they check all addresses, but they are being careful to check files and send the paper to the right place (more work for them otherwise!)
Hang in there.