Three possible reasons, and the third surprises people.
1. A tier actually moved
The health score is four tiers — survival, stability, efficiency, growth — and a weak one drags the whole grade even when the others hold.
Look at which tier moved rather than at the letter. The grade is a summary; the tier tells you what happened.
2. Something ordinary and temporary
A large one-off expense, a customer paying late, a quiet seasonal month. These move the score and say nothing about the business.
Compare against the same period last year rather than last month. Seasonal work makes month-to-month comparison close to meaningless — see health reports.
3. The data got better
This is the counter-intuitive one and it is common right after connecting a new source.
A score built on the bank alone cannot see unpaid bills. Connect your accounting software and it can — so the score now reflects obligations it previously could not measure. The business did not get worse; the picture got complete.
The same happens after clearing a backlog of uncategorised transactions, or after costing jobs properly for the first time. More accurate inputs frequently produce a lower and truer number.
How to tell which one
Connected something recently? Almost certainly reason three. One tier moved and the others held? Reason one, and that tier is where to look. Everything moved slightly? Usually reason two.
Common errors
Do not treat the letter as a target. It is a reading, and a business improving genuinely will sometimes see it fall first as the measurement catches up with reality — see how Omnyra reaches a number.
Your own numbers
This article explains the general case. For what is actually happening in your business — which customers, which jobs, which period — ask the assistant in the Command Center, which can see your workspace. The wiki cannot: it is public, and it has no access to anyone's data.