Extremely slow opening Writer document

Hi all,
I’m running a 18.04 xubuntu box on which was LO 6.0, and I’ve run into an issue: a writer document has suddenly become nigh impossible to open - 5 to 6 hours or thereabout. The first few times, I didn’t wait that long and I just thought there was some problem with the file, but I couldn’t seen any (at the very least, it unpacks with no problem in an archiver).
When finally I was able to open it (I could move back and forth within it, but I couldn’t edit its properties. I didn’t try anything else), my first action was to try and save it under a different name. 24h later and Writer still hadn’t saved it when I gave up on that.

I tried to update to 6.2, but no luck. I did check whether there was some problem with LO, but I could open the ‘Writer Guide’ just fine. Just to compare, my document is 70 pages, with some tables, an index and mostly text in it. Apart from a couple of title styles, I only used linux libertine and biolinum with it. There is one svg image in it (just listing the characteristics in case some known bug has escaped me).

I imagine there is some kind of problem with the file, but I can’t just forget it (I have no previous state copy of it). Is there anything anyone knows I could attempt to do ?

I have the same with a 6 pages doc. Please help!!!

Sorry, but that was quite a while ago. I’m not quite sure what I did.
I believe I managed to find a previous copy of the document and converted it to a master + a number of subfiles. Doing so, I must have broken whatever combination of parameters that led to the problem.
As you can see, nobody ever answered my question, so this appears to be an undocumented bug that is more or less unrelated to the size of the document.