In the order they turn out to be the real cause, which is not the order Google’s own
help pages list them in.
Keywords in the business name
By a distance the most common cause, and the one businesses least expect because an agency usually did it. "Smith Plumbing Emergency 24hr Drain Repair" is not the registered name of anything. Google’s rule is the name on the shopfront, the van and the paperwork, and nothing else.
An address that is not a place of business
A virtual office, a mailbox, a co-working desk, a registered-agent address, or a home with no signage while the listing shows an address. All of these are grounds, and Google checks them with street imagery and with the post.
Too many edits at once
Changing the name, the address and the category in one session on an established listing looks like a hijack, because that is what a hijack looks like. Legitimate rebrands get caught by this constantly.
A category that does not match the business
Particularly in the regulated categories. A general contractor filed as a locksmith, or a marketing agency filed as a lawyer, triggers a review whether or not it was deliberate.
Reviews that look bought
A burst of five-star reviews from accounts with no other activity, or reviews arriving faster than the business could plausibly serve customers. This suspends the profile, not just the reviews.
Duplicate listings for the same business
Often created years apart by different people, sometimes by a previous agency. Google treats several live listings at one address as an attempt to occupy more of the map.
Nothing you did
Suspensions happen in waves when Google tightens a category, and businesses that have not been touched in years get caught. This is genuinely common and it does not mean somebody made a mistake.