No bikes *at all* including folders** on the East Suffolk line (Ipswich - Lowestoft) and Lowestoft - Norwich last year. There were 50 bikes per train (once per hour) from Ipswich to London - 2019 is probably the last year for this service, as the new stock arriving later this year doesn't have a separate brake/luggage van.
As far as Diss is concerned, I *think* it was the usual number of bikes per train like normal. (Well, as normal as Anglia ever gets!)
If I go again this year (4th time in 5 years) I will undoubtedly do what I have done the previous 3 times and head on to Sheringham YHA as a 300km DIYxGPS. This entails a relatively early start (by Dun Run standards) to keep the latest possible finish time before the hostel closing time, but means that I don't have to worry about getting back to London!
** This was a new restriction brought in in 2018, the non-folding bike restrictions have been in place for several years.