That is a common thing with G. It seems to "test the waters" of your schema then disappears for awhile. This is consistent across sites large and small.
Anyways, there is no limit. We have some sites with 30k+ entities. It does take forever to index (or report index in GWT) though. Expect delays up to 8 months if your site is not freshened often. Even popular sites can take 2+ months to get all their schema entities recognized, then another month or so for G to actually put the widgets into SERPS.
PS: Make sure you THOROUGHLY check for errors with the test tool before pushing your schema live. An error will stick in GWT for a very long time. You can attempt to repair with fetch as Google, but it prob wont work. We had errors on some pages that were over a year old...basically a year later G finally revisited and realized "hey they must have fixed that schema snippet". Just be careful.