I cannot reproduce the problem.
I used this file:

After replacing the missing images files, I also could not reproduce the issue with this blend.
My impression is that it is very difficult or impossible to reproduce with simple setups. It might be necessary to use a more real project like in my case 2500 rgba frames in 1920x1080 at 29.97 fps and even then it gets quite tedious, but sometimes the lock-up happened after just one minute.

edit:
It also locked-up using a jpg sequence and without the alpha png on top. It did not lock-up with the sequence only without effect strip, but did not lock-up after adding the speed control again - that's odd.

Have you tried it with a larger project?

Since I am still not sure what is triggering the issue and if continuing to scrub after 10 minutes would trigger it, it is quite difficult and not possible to rule out the issue in a specific version. I could not reproduce it in 2.83.8 in 8 minutes, but perhaps it would have taken 12 minutes, I don't know.

Would using a debug build generate useful output?

Realistically, without a reliable way to reproduce the problem, there is not much what developers can do.

You can try the latest daily build and run blender_debug_log.cmd that is included in the download.
After Blender closes, the logs will be in a text file which can be attached here.
Most likely it will contain more information about the error.

Sorry, I downloaded https://builder.blender.org/download/blender-2.93.0-d91fec1a85d9-linux64.tar.xz but there is no blender_debug_log.cmd included.

With my project, I can reproduce the issue quite reliably in 5 minutes, but sometimes it does not work.
I compiled a debug build and tried it in the terminal: no output on lock-up, so I ran the debug build from QTCreator and as Blender locked up, I clicked Interrupt GDB and copied the stack trace:

1  ghash_bucket_index            BLI_ghash.c       165  0x94a119f 
2  BLI_ghash_remove              BLI_ghash.c       906  0x94a119f 
3  seq_cache_recycle_linked      image_cache.c     980  0x41d1d4c 
4  seq_cache_recycle_item        image_cache.c     1064 0x41d1fc6 
5  seq_cache_put_if_possible     image_cache.c     1396 0x41d2e30 
6  SEQ_render_give_ibuf          render.c          2012 0x41e0780 
7  sequencer_ibuf_get            sequencer_draw.c  1334 0x472318b 
8  sequencer_draw_preview        sequencer_draw.c  1878 0x472464b 
9  sequencer_preview_region_draw space_sequencer.c 716  0x47387f1 
10 ED_region_do_draw             area.c            558  0x41937ea 
11 wm_draw_window_offscreen      wm_draw.c         724  0x3731a69 
12 wm_draw_window                wm_draw.c         864  0x3732016 
13 wm_draw_update                wm_draw.c         1065 0x373264e 
14 WM_main                       wm.c              652  0x372ec29 
15 main                          creator.c         520  0x30fd661

on the second try/lockup, this was the trace:

1  seq_hash_render_data          image_cache.c     735  0x41d161a 
2  seq_cache_hashhash            image_cache.c     743  0x41d1649 
3  ghash_keyhash                 BLI_ghash.c       148  0x94a117d 
4  BLI_ghash_remove              BLI_ghash.c       905  0x94a117d 
5  seq_cache_recycle_linked      image_cache.c     980  0x41d1d4c 
6  seq_cache_recycle_item        image_cache.c     1064 0x41d1fc6 
7  seq_cache_put_if_possible     image_cache.c     1396 0x41d2e30 
8  SEQ_render_give_ibuf          render.c          2012 0x41e0780 
9  sequencer_ibuf_get            sequencer_draw.c  1334 0x472318b 
10 sequencer_draw_preview        sequencer_draw.c  1878 0x472464b 
11 sequencer_preview_region_draw space_sequencer.c 716  0x47387f1 
12 ED_region_do_draw             area.c            558  0x41937ea 
13 wm_draw_window_offscreen      wm_draw.c         724  0x3731a69 
14 wm_draw_window                wm_draw.c         864  0x3732016 
15 wm_draw_update                wm_draw.c         1065 0x373264e 
16 WM_main                       wm.c              652  0x372ec29 
17 main                          creator.c         520  0x30fd661

Hope this helps.

It did not lock up if I used one frame stretched to the whole duration, it seems to be necessary to use a real image sequence.
Since VSE can't pack images, you could try any image sequence you have on your harddisk (please don't delete & create but edit the path in the sequences, just to be sure). If you don't have one, you could use ffmpeg to convert e.g. a blender movie to single frames

ffmpeg -i input.mp4 -t 01:44 -vf fps=25 out%04d.jpg

In the attached blend file, I added more strips in the hope to make it lock up faster, so you would not have to keep trying more than 6 minutes (but that may be hardware dependent).
Please grab the timeline, scrub left and right and randomly all across the screen for at least 5 minutes until it locks up (keep LMB pressed for the whole duration).

In T87090#1141873, @Georg K (georg) wrote:

It did not lock up if I used one frame stretched to the whole duration, it seems to be necessary to use a real image sequence.

What I meant is that I would take 1 image provided and copy it on disk to whatever number of files that is necessary.

I will try to reproduce with data you provided now and see whether I will be able to reproduce the issue.