Hello and welcome
I wouldn't put lemon juice on the bars, it's bad for them.
It sounds like it could be caused by a couple of things, either or both. You say you lift his cage onto the floor. They get very stressed by any change of environment of their cage - even moving it into another room can cause them to go a bit bananas. So it's best left in one place where it lives normally and let him out by letting him walk into the ball from the cage eg. And then letting him out of the ball on the floor.
Also if his cage is too small he will not be happy staying in there. It is probably a combination of the too, assuming his cage is a bit small.
Syrian hamsters need a cage at least 80cm by 50cm of continuous floor area - when the cage is big enough they enjoy their environment in the cage and sometimes don't even want to come out much!
What cage do you have at the moment? For now try weaving cardboard in the bars in the area he is chewing, but he will just move to another area.
For an idea of a good sized cage for a Syrian, the Barney, Alaska and Hamster Heaven cages on this page are all big enough. Anything smaller than the Hamster Heaven could well lead to bar chewing.
https://www.zooplus.co.uk/shop/small.../hamster_cages