Bob n Rharv.
nope. my pc is highly optimised i5 ssd system.
its always been an issue on various systems going back years with rb. irrespective of set up. ive run tests also on powerhouse pc's.
heres the test i just did.
1. imported a biab song. generation + waveform draws took like 30 secs.
2. then i regenned a trak from a gtr rt to a organ rt.
same deal waiting for redraw of new organ trak.
i'm on latest rb 2020 version.

my issue is, in both examples above biab would be off and running /playing way way before rb.

maybe things are diff in rb 21 ?

my songs....mixed for good earbuds...(fyi..my vocs on all songs..)
https://soundcloud.com/alfsongs
(90 songs created useing bb/rb)
(lots of tips of mine in pg tips forum.)