Rarely, a check can't finish: for example when the phone is very busy, or a message is unusually long or unusual in another way. 1krBlocker then plays it safe.
- "Couldn’t finish checking this message, so it was kept aside to be safe" and "Checking took too long, so this message was kept aside to be safe": the message went to Quarantine instead of your inbox, with the headline "We couldn’t fully check this message, so we kept it aside to be safe".
- "One check failed (…); the others still ran": one of the checks failed but the others ran, so the decision is still based on most of the evidence.
What to do: look at the message yourself. If you recognise it and it's genuine, tap Release to inbox. If it asks for money, codes or a tap on a link, treat it as a scam.
If it happens often, update 1krBlocker from Google Play, restart the phone, and if it still happens, contact support with your phone model; we'd like to know.