What you're seeing. "This journal has been submitted for review" or "This journal has been signed off, so no further entries can be added for that day."

Why it happens. Logs feed into that date's journal. Once the journal is submitted, a manager may be reading it; once it's signed off, it's a closed record. Accepting a late entry would change a record someone has already reviewed.

How to fix it. Record it against today, making clear in the note what it relates to, and tell your manager. They can add context in their review comments.

Who can fix it. Your manager — and note they cannot add a log to a closed day either, only comment on it.