I may not have made that clear in OP: But I can still access my wallet in mSIGNA.
Yeah, I get that. My point of importing the seed phrase again was to ensure your wallet is indeed just a single signature wallet derived from that seed phrase and not some more complex multi-sig set up which we would never be able to recover using just one seed phrase.
I see. Yes, good point! I am 99.9% certain it's not a multi-sig. First of I would have remembered and written down some info about it on my seed-paper.
But most importantly, I tried re-importing via the wordlist into mSIGNA and it worked flawlessly - they display a hash for each "keychain" (actually the HD wallet) and it is the same for the imported wallet via SEED compared to my original wallet.
My guess it's only about finding the right derivation path.
Having read through the .pdf again, I'm not so sure:
NOTE: mSIGNA™ always uses pay-‐to-‐script-‐hash addresses, which begin with the character 3 in Bitcoin, even for 1 of 1 accounts.
There is no mention that they use nested segwit addresses, which is the type of address every other wallet will try to recover when given a seed phrase and a P2SH address type. The sentence above I've just quoted suggests they may use some strange custom 1-of-1 script, in which case you will never find it by just playing with the derivation path. You will need to find the exact script being used.
Does mSIGMA have the option to import transactions from elsewhere? That would be the easiest way forward - create an unsigned transaction elsewhere, import it to mSIGMA for signing, and then export it for broadcast. If not, then I think the easiest option is going to be to spin up your own node and get mSIGMA to connect to it. Otherwise you will need to comb through the entire source code to figure out exactly the script type and derivation path which is being used.
No such option available like importing or exporting tx with mSIGNA.
I did check their source code a little bit. Not sure where to look for it and even if I find something how to proceed from there. - Just getting the right derivation path info would probably solve it, right?
About the own node solution: Right now don't even have the disc space for a BTC full node (but could use some older HDD lying around) - my worry is, even after finally having a synced full node running and connected to mSIGNA, the sync process will be stuck somewhere - that's what people seem to report on their github a lot.
Alternatively - have you spend from any of these addresses in the past? If so, we can view the script for them on the blockchain.
That sounds interesting. Would it tell anything about the derivation path or other wallet properties? How does the script used to send help in my case?
Can you guide me through the steps without me exposing my pub keys?
In the end it's around 300 bucks that are unaccessible right now. Would be nice to have, but don't want to spend weeks trying to recover them.
I'm giving away 0.001 BTC for whoever helps the most to recover these funds. Will add info in OP. I reserve the right to decide at my own discretion who will get the funds - if more people are involved in finding a solution I might split it up.
Thanks already for your helpful inpot @o_e_l_e_o .
btw, I edited OP to include link to mSIGNA source code.