Google AdX doesn’t have any limitations but some publishers might have seen warnings after sending too many ad requests per page to AdX.
For instance, “googletag.defineSlot was called without a matching googletag.display call” is one such warning that arises when you send way too many requests.
In fact, other exchanges can also block your requests (or prompt warnings) in such cases. The best way to deal with it is to ensure you have some interval b/w the requests and don’t limit the requests to one exchange. Employ a technique like header bidding and call multiple demand partners, thus preventing you from losing any revenue.