cannot create index in Writer under either Ubuntu or XP (virtual)

I am wholly unable to create an index using LibreOffice Writer 5.4.3.2 under Ubuntu, OR using VirtualBox, also running 5.4.3.2. While I need the index for a large (100+ page) manual, it doesn’t seem to matter how small the document is.

Under Ubuntu:

I will insert say half a dozen index entries, then move the cursor to the end of the document, then call up the Table of Contents and Index/Table of Contents or Index or Bibliography, then select Type/Index, at which point the program simply hangs – it doesn’t matter whether the document is 200 words or 100 pages, as soon as I choose “Index” the programs greys out, with no error message – nor does it matter if I let it sit for half an hour, Writer is stopped dead. I have adjusted memory settings and other settings that have been advised, to no avail.

Trying it under Windows, I find very similar behavior, except the error message

invalid vector subscript

pops up – but again, Writer is stone cold dead.

-RT