Never heard of EncroChat, so let’s see what google says…
Hmm, so it claimed E2E however it was never audited and they didn’t use one of the well known good E2E styles, in addition they sold phones without secure enclave chips nor was any of that audited as well, so yeah I don’t see how it is trustworthy for such communications.
There’s so many ways that such systems can be weakened so it’s not surprising.