I find the Vodafone sim shows full signal but won't stream, it must be network congestion like you mentioned. I'm trying to watch stuff from Dave and they won't let you download. Maybe I need to be less fussy and download iPlayer stuff.
I'm on three and don't get signal at home so need to change network. I tried Vodafone because I get signal at home but can't stream video on my commute. Do any fellow commuters get good enough signal to stream video on Thameslink routes? If you do what network are you on? Thanks in advance!