Houdini Apprentice is working fine.
Then, I may close the app or the app may have crashed.
It does not do it all the time or immediately, but it will eventually.
After that it will never ever open again.
I only see the splash screen then nothing (the app close).
Login out does not solve the problem.
I don't see any process stuck.
Repairing Houdini does not solve the problem.
Only after a full reboot it will work again.

It beginning to annoy me seriously because I need to reboot at least twice a day.
I have the latest Ubuntu version.

Rebooting a Linux is a serious offense.

Also why does downloading color theme inside "Color Settings" always fail with errors?

which version of ubuntu you are using ?
if you are using NON-LTS version of ubuntu , i actually say you must switch to LTS version like 20.04
but in 22.04 sometimes houdini will be crashed

i recommend for you use ubuntu 20.04 ( actually latest of 20.04 ) which now is 20.04.5
some libraries in latest lts ubuntu has no matching with houdini specially glibc library

houdini requires below 2.34 of glibc for running

22.04 uses 2.35
22.10 uses 2.36

i'm using ubuntu 20.04.5 working without any issues

install all xcb libs
if you have nvidia card , you need to install latest nvidia-driver from official nvidia repository


follow nvidia driver instruction :
https://docs.nvidia.com/datacenter/tesla/tesla-installation-notes/index.html#ubuntu-lts [docs.nvidia.com]