You're right. Your issue may have nothing to do with the EGR. It could be a clogged injector. Or a sensor issue.
We're mostly van owners here, not mechanics, so mainly provide advise based on our own or other users experiences.
We can help with fault codes, using VCDS etc. We can advise which are the best wheels or tyres. Or which is the best camping stove!
When it comes to issues with no obvious cause then it's more difficult to provide a suitable solution.
If this was happening to my van I would try an injector cleaner to start with. You can get a bottle from VW for about £15 which is supposed to be quite effective.
Good luck getting to the bottom of it.