I was playing this morning and all was OK, I have gone back to play this evening and about half my chest contents are missing. I note a large increase in gold which may signify I have sold the items (which I didn’t) but there are no merchant return items available. Can you help me get my items back? - Just looking closer I think I may be looking at either a different period of my game or someone elses chest as there appears to be a level limit on the items and stuff that I definitely didnt have in there like low end gems (I only store square minimum, if that).
The season has ended.
Start a new game and look for an envelope icon in the bottom left corner of the screen. Click on it to open it. Retrieve those items you wish to keep before 30 days have elapsed (after which they will disappear).
Read about end of seasons here :
https://eu.diablo3.com/en/blog/22312196/season-14-ending-soon-8-31-2018
The blog is for season 14 but is still valid.
Thanks, that seems to be a resolution, cheers for that, although I will be tidying up for a little while! I will take a look at the noted article.
Sometimes it seems that some D3 players are living in a cave and very seldomly get out to see what is happening outside 
Be nice… OP is a new player and the learning curve can be quite steep.