Is there a file size limit on imported books from Kindle for PC?

[MorganAndMerlin]

Im using Kindle for PC 1.25 and Calibre 5.14 with DeDRM that has worked beautifully for the last 300+ books in my library.

But now I'm trying to convert a huge book file. Think text book/encyclopedia size.

When it imports with DeDRM, it imports as MOBI, even though the incoming file is .azw

If I turn off DeDRM, it comes in as .azw (but obviously tells me that the file has DRM)

But regardless of all that, if I try to open the MOBI file, I have the cover and then literally nothing. just 0% at the bottom right corner for the percentage of where I am in the book and cannot progress because there's nowhere to go in the book.

Tried to convert to EPUB and got a popup saying that the file was too large and said to make the size of cuts(?) larger. I went to EPUB outputs and kept uping the size section until it successfully converted. Except the output file was the cover of the book and then nonsense characters for pages and pages and pages.

I've deleted and reimported. I've deleted the book from kindle and redownloaded. Turned off and on. Exited. Every combination thereof.

Send help.