@zarski wrote:
...raise the non delegable item limit from the default 500 to 2000 items...
...The studio show's no delegation warnings or errors.
I wouldn't rely on the yellow triangle warning always showing. There is no such thing as a "non delegable item limit".
The limit you refer to is called the Data row limit.

The data row limit is not limited to the context of delegation. When you use a formula, like say, ClearCollect , Set or any other function, the number of items returned by this function is going to be, at most, the data row limit. No warning is shown when this happens, because there is no delegation issue here, just the data row limit - so no warning is issued if something, e.g. a Collection, or anything else, is expected to have more Records than the data row limit - and yet it doesn't. Each time Collect is called, for example, the amount of Records processed each time it is called, would be no more than the Data row limit. Also consider the example of ForAll which itself returns a Table. The Table returned by ForAll would itself also have no more records than the data row limit, and no warning is shown when this happens
While using the Items property of a Gallery may cause there to be some different behavior, since Galleries themselves just work differently, and certain aspects of Galleries cause them not to have the data row limit applied to them - the rules described above, generally apply anyway.
However, if you are saying the behavior has changed then there may be an issue.
I would recommend in your case to
Create a new Power Platform Support Ticket
in case there is some issue for you and to get more personalized help on your issue.