Email Disappeared after Undo Send-Sequoia 15.5

This is not the first time this has happened. On using the undo send function, rather than the email reappearing as it does 9 out of 10 times it simply disappears without any obvious trace. It is not in my sent folder, draft, junk or bin.

When this has happened before the email has from nowhere reappeared quite some time later for no apparent reason.

I followed a previous post from 2023 but it was closed, but the issue certainly remains. Please help