I found the log in %appdata% so here is the last few lines from clicking on folders - these have almost no images in them yet we can see it's taking 8 seconds to build them!
Init.c(1701): @ 50.141( 0.016) [Startup] Initialize shell icon and thumbnail access
tp8ui.cpp(158): @ 50.157( 0.016) [Startup] Show, place and update main window pane
Thumbs.c(1335): @ 50.188( 0.031) [Trace] Refry file list; flags: 00000012
>'E:\Pics'<
overlord.cpp(249): @ 50.235( 0.047) t7480<Overlord> [Trace] Startup cleared 50.219 seconds after start
Thumbs.c(1472): @ 58.407( 8.172) [Trace] Built file list in 8.219 secs. 32 files (32 total), 34 thumbnails (34 total)
Thumbs.c(1335): @ 299.578(241.171) [Trace] Refry file list; flags: 00000002
>'E:\Pics\Blk'<
PropPane.cpp(257): @ 299.594( 0.016) [Startup] Expanded Info Tab categories initialized. Expanded items: 3. List size: 15 chars. Items = ';Info;Metadata;'.
Thumbs.c(1472): @ 307.813( 8.219) [Trace] Built file list in 8.235 secs. 47 files (47 total), 47 thumbnails (47 total)
Thumbs.c(1335): @ 315.828( 8.015) [Trace] Refry file list; flags: 00000002
>'E:\Pics\Clb'<
Thumbs.c(1472): @ 319.953( 4.125) [Trace] Built file list in 4.125 secs. 0 files (0 total), 0 thumbnails (0 total)
Thumbs.c(1335): @ 319.953( 0.000) [Trace] Refry file list; flags: 00000002
>'E:\Pics\Col'<
Thumbs.c(1472): @ 328.282( 8.329) [Trace] Built file list in 8.329 secs. 202 files (202 total), 203 thumbnails (203 total)