One of the main problems is that the problems are so variable ... one gadget may cause a problem ... another none ..... and the situation vary in a different aircraft ..
For instance we have used various models of a particular make of video camera for flight test purposes and never once experienced a problem .... another camera installation may well have presented difficulties ..... and, indeed, those which we used might well have presented problems in another aircraft.
The problem is not so much that there is a problem .. rather that the line operating crew may be caught out with unexpected problems for which no certification investigation has been made.