When you have added something in "edit" mode it should remain there for both paid and free sites provided you have clicked on SAVE on the page before leaving that page.
If you have not clicked on save your new data will not appear next time you look. That is the only explanation I can offer. I have never experienced any problems such as you write for a paid or free site. I am sure that if you added information and clicked save it would be there next time you looked. That is provided you have the sole editing rights for your tree. Family members can edit their own names and immediate family.
I'm pleased you posted this, as I too have had a similar experience. I have a paid site, always save (and backup) my work, and occasional export it to other programs.
I discovered inadvertently that I am missing a whole family of children. Yet I know I had successfully added them way back, as my other programs will clearly attest. How long they have been missing, I do not know. So I've had to re-enter them using my own backup records. There are no "orphaned" duplicates for these children.
I never overwrite my tree with new gedcoms.
As we have learned in recent postings, there is no mass delete option. Deleting any individual has to be a deliberate act.
The only alarming conclusion I can come to is that TP, the custodians of my data, are responsible for some of it to disappear. Scary.
I wonder if it reduced the stated number in your tree at the same time the names went missing. Not that I will keep a watch on that myself for my site. Something that we should never have to do.
I lost my complete home page on one occasion. My fault as I was trying to add something to the banner that I never expected to be able to add but I thought I would give it a try. I never expected that playing with the banner would delete the whole home page but it did and I don't know how this could happen as the banner and "about" sections are separate for editing and saving. Numbers #1 and #2. Fortunately I had some data in other free sites to copy so it did not mean a complete re-write. Ever since then I have kept a back up of the home page of my paid site.
The moral of all this is, back up everything you can. You say that you do this. With missing names however it is always going to be time consuming to replace these unless a complete new Gedcom is loaded. Like you I use my Tribalpages paid site gedcom as my master copy and always keep a back up copy.