Restaurants judged in their first weeks are being judged on a version of themselves that will not exist a month later. The opening period is an operational shakedown, and almost everything about it is provisional.
Nothing has been tested at real volume
A kitchen can rehearse dishes for weeks and still not know how they behave when forty orders arrive within ten minutes.
Prep quantities, holding times and the sequence in which components are assembled all get rewritten in the first fortnight of actual service.
Until that happens, the same dish can leave the pass in noticeably different states depending on how busy the room was.
The staff have never worked together
A new team is usually assembled from people who have not previously cooked or served alongside one another, in a room none of them knows.
Coordination between kitchen and floor is learned rather than instructed, and until it exists, timing between courses drifts and tables wait.
Turnover is also highest in the opening weeks, so the team being observed may not be the team that settles in. Openings attract staff who want the experience of one, and a proportion leave once the novelty and the long hours have been weighed against each other.
The menu is deliberately provisional
Opening menus are typically longer than they will remain, because the operator does not yet know which dishes sell and which slow the line.
Items are removed once the data arrives, and the ones that survive are refined with the benefit of having been cooked hundreds of times.
Judging a restaurant on a dish that will be gone in six weeks describes a decision the kitchen has already reversed.
The room itself is still being adjusted
Lighting levels, music volume, table spacing and the flow of staff through the space are settled by observation once people are actually in it.
Equipment problems also surface under load, and a walk-in or a dishwasher failing during a first month affects everything else that evening.
These are ordinary teething issues, but they are indistinguishable from poor judgement to someone eating there once. A diner cannot tell a design decision from a temporary workaround, and the restaurant has no way to explain the difference at the table.
Soft openings exist to absorb this
Many restaurants run a period of limited service, reduced menus or invited guests specifically to make these mistakes with lower stakes.
Where that period is skipped, usually for financial reasons, the shakedown happens in front of paying customers and reviewers instead.
Professional critics conventionally wait some weeks before visiting for this reason, which is a convention worth borrowing when deciding whether to book.