It happened again that a (Markdown) document in one of my databases didn’t show up in the search on my iPhone, despite that fact that I could see and open the document on the very same iPhone!
So as suggested in Searching for "an universal" in DT3 and DTTG I tried a reindex: Go to Help, go to Reindex, then to the Execute link - and nothing happens. Same as last time I wait a bit, kill DTTG, reopen it - and still the doc doesn’t show up in search. 
So I try the procedure again. Still no bezel or any obvious indication that a reindex has started. But after closing the help screen a very thin line between the bottom icons and the main item list starts very slowly to grow - Is this the reindex indicator?
Why did this line not come up the first time? Maybe I just overlooked it in its faintness? And why do I have to reindex after a few weeks already again?
A more practical question: When this line is growing, can I switch to other apps or not or what?
Update: After quite a few minutes staring at this growing line (and not touching the phone at all) the line filled up completely and then it showed the bezel “Documents indexed”. Even better I find the document now!!! - However I’m still weary and unclear how to do the reindexing reliably…