The vast majority of so-called 'aerial specialists' have no formal qualifications and little, or no, understanding of the factors affecting the propagation of TV signals. It's not unusual for them to spout total rubbish and your guy seems to be doing exactly that.
The problem is clearly related to insufficient signal strength. Given that you get a good enough signal some of the time, there's quite a good chance that simply using a cheap signal booster will fix the problem. Otherwise replace both the aerial and (just as important) the cabling that links it to your TV sets.
For a more detailed explanation, please read my post here:
http://www.theanswerb...y/Question789132.html
Chris