I have never heard of a maximum epub size. I do have a 5.4MB book that has over 400 chapters in it. The book doesn't have a cover in it, so that is just text. I have bigger epubs, but they have pictures in them and not as many chapters.
It is more likely that there is a problem with the epub and the firmware cannot process it properly. When you put the epub on the device and disconnected, it should have been processed and the details of the book put into the internal database. This database is used for the library lists. This can fail if any book in that batch of new books will not be added to the database. If this is the case, you will need too take all the non-processed books off the device and add them in small batches, or singly, until you work out which is at fault.
As you are using calibre, you could strip the DRM and then do an epub-to-epub conversion. This will usually remove any errors and the books will load. Or, you could use the Epub Split plugin to split the collection into the individual books. This would probably fix any problems as well.
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