Simple, single, 28.2 as you described is correct for the tuner connected to universal output of dish pointing to 28.2. Might be better for you to also post your screenshot so someone can double check.
For the Terrestrial one, set it to UK all regions. That is good enough for most people.
Manual scan gives you more control of what you scan instead of automatic. You can even go through the transponders one by one. Can also do that with Signal finder.
Surely it is is easier to recheck the Gigablue instead of going up into loft? When fault finding, you generally start with the last thing that changed. On another forum, somebody went through all the elimination stages, it turned out that the f-plug had worked loose when they swapped receivers.