Okay I'm sorry if this is a saga of the bleeding obvious to experienced 12 string players, but actually your comments are making me think my way through my thoughts.

So I've sent for the EJ41 strings that are the only ones recommended so far.Along with it, I sent for   extra 9 gauge strrings, also recommended.

When I was looking at the various g, which is generally a huge ask of a string's tensileauges. I noticed that the string doubling the covered G was the same gauge as the first string.

So the thin G is being asked to be two semitones tighter than an E, which is generally a big ask of the string's tensile strength. No wonder that it is that string that has broken. So easy to tune sharp those strings anyway.

Okay any more thoughts from you 12 stringers, before my new strings arrive and I start thinking about what move to make next. I think I may attempt to tune down two semitones.