@tgodfrey wrote earlier:

I have each collection in a separate subdirectory,

Not sure what you mean? I have a dozen collections but they use the same database. The only folder issues are a) I have unique folders, like stubs, with an [index.php] so I can call them from [thedomian.xxx/collection_name] and b) there are the media folders that are automatically created

Thank you amoun for your reply. Yes, I have the same situation, but the second and third collections (of 3) display the sitewide header, even though it is turned off. I can deal with it by logging in to admin with a different browser, so maybe I should just do that. Yes - why would that be a sessions issue? Anyway, I don't wish to consume anyone's time/energy. Problem solved. Thank you.

page cache issue?

No, I checked that a few times after logging out, logging in, etc. I don't know whether this has any bearing, but I am loading the 3 collections on one page, each in its own iframe. Worked without issue until recently, I think.

With the cache issue. The logging out and in I think is only the browser cache, which have set to delete at each new start, but I think there's a server cache which saves recalling php bits and bobs.

Ah yes. I've been thinking about the same thing. There is major internet connection stuff going on here at present. Some odd stuff happening from moment to moment, but I suspect you are right amoun. I will go back to basics and see what I can isolate.

Thank you chaps.

URL?

I've done nothing at all in the intervening period, and today all is well. Sitewide switch functions across 3 collections, and turns off and on without clearing any cache. There is this sort of stuff going on locally at present:

https://forums.whirlpool.net.au/forum-replies.cfm?t=2526460

Perhaps weirdness should be put down to that.

Err, I don't see a problem with this page. perhaps more URLs and screenshots of good vs bad?