GMB drastic drop in positioning

[Alessio1979]

Good morning... these days I'm noticing a drastic drop in positioning. Example from the second position for a keyword that interests me I moved to 8 or 9. The only thing I noticed was that 3 or 4 reviews were deleted. Nothing else has been changed. I know there has been an algorithm update and the only thing I can think of is the loss of these reviews or the fact that I use (keyword - business name)
Question...the changes are practically published immediately but how much time must pass to see the effects of the change?
My GMB :
Centro Estetico Treviso - Karinya Academy
Centro Estetico Treviso - Karinya Academy - Cerca con Google

 

[Colan Nielsen]

On what date did the drop in rankings seem to happen? There was a significant algorithm update in October that impacted the local algorithm.

 

[Alessio1979]

It all started around September...I honestly don't know what changes to make anymore! Every week I publish new posts, new quality images….maybe I have a few new reviews. But the usual companies maintained their positions... so I doubt it's the algorithm! I really don't understand...

 

[Colan Nielsen]

How much time and effort have you put into the page on the website that you link to from the GBP? I can't tell you how important that page is. Make that page amazing and it typically has a drastic impact on your local pack rankings.