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It does sound like a dodgy rims tape being the problem, even if it doesn't look like it when looking at the holes.
Hopefully that should solved it, failing that, a new tyres might be needed.
(Plus I really can't tell any difference between cheap inner and expensive one, I personally don't think it make that much of a difference unless it's a bad batch that made it pass QC, which also happen with a Schwalbe set once!).
The rim tape is arguably not the best; it's plasticy, that's why I'll be getting new ones tomorrow as well. Every time I had a flat, I checked the tyres and rims and they we're pretty much spotless.
I've lost count/memory of where the holes were. Last one was on the inside of the rim, so where it touches the rim tape/valve holes (which would indicated shoddy rim tape?). The last hole was tiny which deflated the entire tube in under 10 seconds.
I'll be getting some better rim tape and tubes and will thoroughly clean the rims and tyres and we will try again.