Thanks everybody for the replies.
@Zappoman with regard to the backups, I get that the daily backup wont fire with every change, but it should fire at the end of the day, and I am watching the half hourly while I work and have made many additions and deletions over a period of hours yet the halfhourly never updates since 3 weeks ago. I have checked the rules and they are ok. I have resorted to manual backups for now.
The objects that disappear are quite often large ones, 150 x 150 ground surface simple flattened cubes with texture, and locked. Sometimes I find it at the origin and it is tiny, it is about the size of the little red ball at origin, several times objects have mysteriously gone to the origin and shrunk, in these cases I can restore its size and location manually, once my entire venue of 7M and 80mtrs across moved itself to the origin but was huge like 2000mtrs across, again I could restore it.
Months ago I had some trees that would disappear, and house that would disappear regularly, I had a bad script in the domain and blamed that. I cleaned the stack and started fresh, it was good for a couple of months then when voxels were removed I added these 4 big grass floors and locked them, and one of them, usually the same one, would disappear, and the list would only show 3 (I then go to the origin to see if its there, its not) but this most recent time there was 4 on the list and I thought it was finding the same one twice but turned out that there were 2 in the same place, it had moved back to the place I duplicated it from, like undo.
They were all locked so I had to unlock one to move it back.
It wasnt missing it was moved
On another server the entire city of venice turned into a cricket ball at the origin, it was restorable, but the next day (yesterday) it was gone completely, not even in the svo file, in fact the svo file had reduced in file size and the text was visibly smaller. I restored the city from the models. There have been no scripts on this server.
They have been locked but I have just recently enabled trusted editors and will watch closely. Someone would have had to unlock it to delete it.