I'm interested in this matter although it wasn't publicly announced.
My opinion is ISX would have been unable to list on the LSE (even if it met the listing requirements) without first delisting from the ASX, so ISX could not have been listed on LSE by April 2021.
The Frankfurt listing (TA8) is just a secondary listing and is totally different from this one. That's why it's been suspended there since being suspended on the ASX.
ISX Price at posting:
$1.07 Sentiment: Buy Disclosure: Held