The screenshot below shows the volume of unique visitors for eVar1 and the page dimension for the same page name.
We have one s.t() call on the page sending the page name to both s.pageName and eVar1. There are a couple of click events on the page, but these fire s.tl() calls so should not inflate the metrics like visits, unique visitors, page views etc. for eVar1.
As you can see, eVar1 unique visitors are generally much higher than unique visitors to the page dimension, until a point in early February when they match up (which should happen anyway).
We only started seeing this mismatch when we migrated to Launch so when things aligned again in February it was a pleasant surprise.
This appears to be a blip because since the last week of February, the unique visitors for the eVar are outstripping the unique visitors for the page once again.
I have to stress, there have been no configuration changes in Launch affecting the page in question. No new events, no changes to existing rules etc. Nothing. There have obviously been changes to our overall Launch configuration (i.e. rules modified or added to other parts of the site), and dev releases to our site, but nothing that would directly affect the Launch code or have an impact on how Analytics itself processes s.t() or s.tl() calls and calculates metrics.
This issue does not affect all pages on our site, and it seems like the only commonality between affected pages is that there are events triggered on the page itself.
I appreciate there is a lot to unpick here and more information will probably be required, but this has been bugging me for months.
Note that our site isn't accessible outside the UK if you want to do some QA.