This bug appears to be related to Bug 93261 - Persistently high background CPU usage by soffice.bin with high-word-count Writer document.

In LibreOffice Writer 4, the word and character count displayed in the left of Writer's statusbar would periodically update in real time shortly after a document was loaded, letting the user know that Writer was (apparently) repaginating the document and updating its statistics in background. Sometimes the display update would be paused or interrupted if the user initiated a task (e.g., switching sidebar panels) before the background repagination/statistics updating was complete, but the word and character count would generally display correctly once the task was complete and focus was returned to the document's main frame.

When a high-word-count document is loaded in LibreOffice Writer 5.0.0.5 for Windows (both x86 and x64 editions), the word and character count DO NOT update in real time, and in fact do not appear to update AT ALL until the user has engaged in some foreground activity in the main document frame, e.g., by editing, initiating a spell check, jumping to a bookmark, or jumping to the end of the document. (Significant scrolling seems to trigger a statusbar update but minor scrolling does not.) The word count and character count typically start out by immediately jumping to (very roughly) around 1,700 words and 10,000 characters, and they remain at those initial numbers until the user engages in foreground activity.

Word and character count automatically update within a reasonable time (albeit in a single jump, without intermediate refreshes) for ~14,000-word and ~70,000-word documents. They NEVER update on their own (without user activity) for ~430,000-word, ~570,000-word, and ~720,000-word documents. The bug can be tested on the documents I uploaded for Bug 93261. 

This bug, in itself, is only a minor annoyance -- the user doesn't know when Writer has finished repaginating and updating statistics in background -- but it's a clear regression with respect to LibreOffice 4. That said, I suspect it is connected to another bug I noticed in LibreOffice Writer 5.0.0.5 (Bug 93261 - Persistently high background CPU usage by soffice.bin with high-word-count Writer document). Is it possible the initial background repagination/statistics-updating routine gets stuck in a loop in high-word-count documents? If so, manually updating document statistics (File > Properties > Statistics > Update) doesn't seem to break it.