There's a chance here that Blockchain messed-up the WIF private key's encoding where it should be without the compressed byte flag.
Nice catch!
Thanks!
My guess came from the fact that they used private keys in bare base58 format (
without the checksum and network byte) instead of WIF.
But in their new wallet version, all imported and migrated non-hd keys are displayed in compressed WIF form.
Probably a simple conversion from base58 to base58check with the compress byte regardless of the public key used to generate the address.
Thanks so much @LoyceV @nc50lc and everyone that helped - I think that worked!
You're welcome.