Irritated by the 10+ seconds it takes to open the layout menu (MBP i7 with SSD) I decided to delete the layouts in the RHS of the menu.
The bottom line is that my menu now opens almost instantly 
An Observation:
When saving a layout, I assumed an independent copy was stored somewhere, and a link to it appears on the LHS of the menu. This does not seem to be the case. When you delete the last remaining instance of a named layout (on the RHS), then the layout also disappears from the LHS without warning! I would guess that the LHS list of saved layouts are only shortcuts to the stack of layouts on the RHS.
Suggestions for Logos (please
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1. It seems that Logos is making snapshots at all sorts of time without pruning them. I wonder how often we return to a snapshot/app close after a month has passed? two months? a year? Please prune these automatically.
2. Please implement a warning if the last instance of a named layout is about to be removed.
The other menu plagued by appalling response times is in the search/library panels. I want to search subsets of my resources, as defined by my collections. If this is the same as the layout menu then I would put the number of entries in the menu as the cause of the lack of responsiveness.
A Final Suggestion (
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3. The search/library menu should not be populated with an entry for each tag (I have hundreds) plus ratings, series etc. I cannot 'delete' these ... I can only request that Logos stops putting them there, even if it is an option in the settings ...
Thanks.