Where reviews actually go.
Five causes explain nearly every disappearing review, in roughly this order.
Google's spam filter (the big one)
Automated detection removes reviews that look inauthentic — posted on your Wi-Fi, from new or thin accounts, in bursts after a promotion, or via a review kiosk at the counter. It's aggressive, and legitimate reviews get caught.
The reviewer removed it — or Google removed them
People do delete their own reviews, and when Google shuts down a spammy account, every review that account ever left vanishes with it, including the real one they left you.
A content policy flag
Reviews containing links, phone numbers, profanity, or anything reading as off-topic or promotional can be pulled — sometimes weeks after they were posted, which makes the removal feel random.
Your profile changed status
If your profile got suspended, merged with a duplicate, or re-verified after an edit, reviews can hide or vanish in the shuffle. If ALL your reviews disappeared at once, look here first — start with the suspension guide.