SCHEDULE post malfunction

I’ve never had trouble Scheduling posts before. Then 2 didn’t post and I had to manually publish them after their time. Then we got a new version of WP and the next one posted. I thought it was fixed, but this morning’s didn’t post.

Is it a bug in the system or something at my end?

I’ve checked the troubleshooting and my time zone is fine and I always do the same thing – add a time, click OK, and click Schedule. It shows as “publishing on the right date at the right time” but stays there even after the time has passed.

Not much of a techy – can anyone help here?
Thanks.