I wish I had an answer for you,why do cats do what they do...
Maybe the floors have been treated with something he likes the taste of
Maybe the plant??
I just discovered my cats like to lick photographs,of course I did not let them,fearing something toxic.
You mentioned your cat was unhappy after you left home,but maybe the move to your house upset him,although he's happy to be with you
Cats are very sensitive to any changes in their lives..
However if he stops eating or shows other symptoms a vet-visit will be needed.