More Tag malfunction

I am now having the old MoreTag problem on multiple sites running version 2.1.3. Until recently the split was working just fine. Now, suddenly, it shows in the editor but not in the published post or even in the preview area. This happens regardless of whether I use rte or not, visual or code. And nothing has changed code-wise from my end – no recent changes to the files other than to add a line for wp-ads and I think this happened well after Ads was sucessfully implemented, but that was on only 1 site. Also, it is happening to sites using different themes (RoundFlow and Tiga to name 2).