I’m sorry to hear about your client website being taken offline. But it also has nothing to do with the theme. There’s nothing in the theme that adds something to the content table. The only time something gets added to the table is when you create posts. The theme will only read from that, not write to it. No other buyer has had this problem before as well. I’ve moved around our demo a couple of times, and I know how big all the tables are, but none of them come even close to 346.000 entries. I’d recommend reinstalling WordPress completely and see if that solves the problem. I’m sorry if this isn’t of any help, but I know for sure this issue isn’t with our theme.
Good luck with the website!