Anyone experienced on how to solve a DMM (of medium quality not top/best one) failing to meter DC voltage unless after probing several times later or perhaps just waiting a minute or so later, after which it will work normally for the needed measurement

 

Check the probe sockets on the meter, I had one where the connection was iffy.
The solder from socket to board needed attention!

 

If it is the kind which has a big rotary range switch, try twiddling that back and forth. The contacts there are not always reliable.

 

A bit more info on the meter would be helpful for sure. You might try tapping on the meter as you measure something to see if you get a jump or loss in the reading, and of course what's been mentioned is a good place to start also. Good Luck.