Andrew, not sure but I think running Valgrind with lv2 plugins is just problematic -- it has never been run that way here.  Lv2 was sort of implemented separately from Cinelerra as opposed to an integral part.  I can only suggest going into Settings->Preferences, the Interface tab and temporarily remove "Default LV2 path" (you may have to disable the environment variable too).

Now, I have some crash at lv2 plugin scan under valgrind, but this may be also false positive:

---------------

root@slax:/home/guest/botva/src/valgrind/valgrind# rm -rf ~/.bcast5
root@slax:/home/guest/botva/src/valgrind/valgrind# valgrind /usr/bin/cin
==8414== Memcheck, a memory error detector
==8414== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==8414== Using Valgrind-3.16.1 and LibVEX; rerun with -h for copyright info
==8414== Command: /usr/bin/cin
==8414==
Cinelerra Infinity - built: Nov  1 2020 10:30:54
git://git.cinelerra-gg.org/goodguy/cinelerra.git
(c) 2006-2019 Heroine Virtual Ltd. by Adam Williams
2007-2020 mods for Cinelerra-GG by W.P.Morrow aka goodguy
Cinelerra is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it under
certain conditions. There is absolutely no warranty for Cinelerra.

==8414== Syscall param ioctl(generic) points to uninitialised byte(s)
==8414==    at 0x58B3734: ioctl (in /lib/libc-2.30.so)
==8414==    by 0x5D25F3C: drmIoctl (in /usr/X11R7/lib/libdrm.so.2.4.0)
==8414==    by 0x5D28A53: drmCommandWriteRead (in /usr/X11R7/lib/libdrm.so.2.4.0)
==8414==    by 0xF78F524: nouveau_object_ioctl (nouveau.c:88)
==8414==    by 0xF78F754: nouveau_object_init (nouveau.c:262)
==8414==    by 0xF790147: nouveau_device_new (nouveau.c:389)
==8414==    by 0xD0CA470: nouveau_drm_screen_create (in /usr/X11R7/lib/dri/nouveau_dri.so)
==8414==  Address 0x79e7982 is 2 bytes inside a block of size 72 alloc'd
==8414==    at 0x40335CC: malloc (vg_replace_malloc.c:307)
==8414==    by 0xF78F6EF: nouveau_object_init (nouveau.c:251)
==8414==    by 0xF790147: nouveau_device_new (nouveau.c:389)
==8414==    by 0xD0CA470: nouveau_drm_screen_create (in /usr/X11R7/lib/dri/nouveau_dri.so)
==8414==
init plugin index: /usr/lib/cin/plugins
PluginFFilter::new_ffilter(overlay_opencl)
  err: Ошибка ввода/вывода
PluginFFilter::new_ffilter(xfade_opencl)
  err: Ошибка ввода/вывода
[frei0r_src_736 @ 0x12ac2bc0] No filter name provided.
PluginFFilter::new_ffilter(frei0r_src)
  err: Недопустимый аргумент
[openclsrc_752 @ 0x73202c0] OpenCL source requires output dimensions to be specified.
PluginFFilter::new_ffilter(openclsrc)
  err: Недопустимый аргумент
init lv2 index:
LOAD: http://lsp-plug.in/plugins/lv2/comp_delay_mono
shmat: Недопустимый аргумент
==8414== Invalid write of size 4
==8414==    at 0x8657FCC: PluginLV2::init_buffer(int) (in /usr/bin/cin)
==8414==    by 0x8657E5C: PluginLV2::init_lv2(PluginLV2ClientConfig&, int, int) (in /usr/bin/cin)
==8414==    by 0x865BE0D: PluginServer::new_lv2_plugin() (in /usr/bin/cin)
==8414==    by 0x8662041: PluginServer::open_plugin(int, Preferences*, EDL*, Plugin*) (in /usr/bin/cin)
==8414==    by 0x865BFDF: MWindow::init_lv2_index(MWindow*, Preferences*, _IO_FILE*) (in /usr/bin/cin)
==8414==    by 0x86145E2: MWindow::init_plugins(MWindow*, Preferences*) (in /usr/bin/cin)
==8414==    by 0x861D4DF: MWindow::create_objects(int, int, char*) (in /usr/bin/cin)
==8414==    by 0x85DCAC3: main (in /usr/bin/cin)
==8414==  Address 0x8 is not stack'd, malloc'd or (recently) free'd
==8414==
** segv at 0x8657fcc in pid 8414, tid 8414
writing debug data to /tmp/cinelerra_8414.dmp