Word 'mega' Headache

[Kramerica]

 🤬Every Word user will know of the navigational box I am referring to [see image below if you are unsure]  (which upon opening any document is close to the vertical scroll-bar and reads: welcome back, pick up where you left off) this can also be performed by the keyboard shortcut Shift+F5.

Only some of my short Word documents feature the navigational box, while other more lengthier documents don't have this feature at all. On the other hand - not even 1 document (long or short) will recognise Shift+F5 Is there a setting in word which will enable this key combination to be recognised?

Some short documents have this feature for only a short time.

I can already predict what every response to this query will be - that you do have the navigational box;  or that Shift+F5 works for you - it works on your system.

Please note everyone - I am not asking about your documents. And if you research this navigational box absence issue, you will discover that it is a extremely rare happening (in other words - I am not dreaming or going mad)!

Does anyone have the solution to making the navigational box apply to every Word document permanently. This exact same scenario happened when I was using Office 2013 on a different laptop.

Today I have uninstalled and reinstalled Office 2019 - with no luck.

Thanks in advance.