Why reviews drop without negative reviews

[ValaraAtranCrafts]

Hello. 
I’ve been a seller for a decade, and only 1 review was 4 stars - and it is still. It made my Average Star rating at 4.9. 
Today I noticed my Average Star rating fell to 4.8. There are no more reviews that can possibly put it lower.

Why did it happen? Can the support team fix this? I don’t think it’s fair. There was no notice of reassessment - nothing.

Out of total 33 reviews - all are “5-star” reviews and only one “4-star”. So, instead of 4.9 it suddenly (after 10 months) became 4.8. Again - no other dissatisfied review posted

[GieseDeseiGns]

because some of your 5* reviews fell off, it is a 12 month pattern so if you only had say  2 5* in one month and 4 fell off from the previous month your rate would be lower.

[audreytherese]

I agree, it's the rolling 12 months that you are seeing. Today is December 18th, which means the 5 star review from Victoria on December 18th last year was just removed from your metrics. 

The average is only looking at the past 12 months, so it's only counting 6 total reviews, not your shops 33 lifetime reviews. Out of those 6 only 5 were 5-stars. 

[Adorabilities]

They're not going to notify you of a reassessment -- your overall shop's star rating is calculated every day.

[VintageRescueSquad]

Do the math: write down how many reviews you've had since Dec. 19, 2022, add them up, and then divide by how many. It's pure math. Only reviews from the last 364 days count towards your overall rating.