The sluggishness I've experienced isn't tied to any particular layout. The standard layouts as generated from the help-menu behave the same as my custom layouts.
I was hoping for other users in the community to chime in with their experiences before reporting anything into the bug-tracker. It would be interesting to hear from more users if they have seen anything similar, and which tablet-models and software they were running.
I've experiences "sluggish" layout processing on the following units:
- Samsung Galaxy Tab A (SM-T-580) / Android 6.0.1
- Samsung Galaxy S4 active (GT-i9295) / Android 5.0.1
- Lenovo Tab 3 / Android 6.0.1
- ASUS Nexus 7 (2013) /6.0.1
A couple of these are getting old, but the layout processing does seem equally sluggish on all of them.