Tracked down why some of my grids only have a single record in, but work fine with a page size of one, or by changing the sort order.
The product I am attempting to update to 4.1, and likely any product we will write in the future, is multi-tenanted, a common thing with SaaS products I'd have thought. To determine which client data is for we use 'clientId'.
So, with 4.1 I suspect we're going to have to have a base model that changes this clientIdProperty to something obscure (phantomId perhaps?), for functionality that we don't use (we never create phantoms on the client).
Oh well, just thought would post about it in case anyone else has a similar issue.