Today we released a hotfix for SentryOne Plan Explorer The following two fixes were included in the update (change list here):
In 18.5, we made it possible to see statistics histograms in more scenarios, such as the leading column for missing indexes, or any candidate column that has its own statistics. If you opened an older session file which had been saved with a column selected in the Index Analysis view, the UI made it look like an index was selected. But the histogram wouldn't show until you changed your context away and then back again. We've fixed that so the right context is triggered on open. As an added bonus, we will "borrow" the index statistics and histogram for any leading key column, so that they show whether you highlight the index or the column. We won't be able to show column statistics for columns that have stats but aren't the leading key column in an index, since earlier versions of Plan Explorer didn't collect that info.
It seems like the moment the SSMS 18 Preview was made available to the public, the requests for our add-in to be supported started rolling in. We knew this was coming, but it just missed the cut for our more substantial 18.5 release. Now you will be able to open an SSMS plan in Plan Explorer from within SSMS 18, though I will still always urge you to just generate your plans from within Plan Explorer in the first place.