Never done a map on a
Ibiza but on my Leon my mapping company were very clear what was needed, and for stage 1 that was nothing other than the map itself. You can always add a bit extra with cold air intakes but on the Leon the stage 1 map I had would not support bigger exhaust
Further the fact sometimes it works and others it dont could be down to the software wanting the engine / oil to be at a certain temp before full power is provided (thats is what i have on mine anyway) and also if the engine / oil is over hot same thing. But your mapping company should have advised you about that when installing.
I would also not make any changes if you are taking it back if you have change stuff they have wiggle room.
What I would suggest if try and note if there are any specific conditions when you dont get power and when you do so that it narrows down the issue.
I appreciate this dont
help but any decent Mapper should be more than happy to solve the issues with little drama and if they wanted you to change your cars setup to work on this map (which dont make sense as its on off) they should have advised you of this up front.