It doesn’t surprise me with the Celtic box of tricks. These newer ECU’s are increasingly hard to tune via ‘on the fly’ type OBD programming modules. One of the reasons I went to add on tuning boxes with my mk7’s which are far from ideal.
You can’t go wrong with REVO. They were amongst the pioneers of OBD tuning for VW group cars and have a worldwide network of testing, tuning and everything that goes with it.
I don’t know if the same guys are behind the company as when I first became familiar with them (a long old time ago now) but amongst them was Mark Yates who had a lot of VW fast road and motorsport tuning pedigree.