Comment 3 for bug 1806459

Found this (Debian) thread, which suggests the root cause is the JIT:
"JavaScriptCore JIT compiler crashes in x86", https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=899338

Package: libjavascriptcoregtk-4.0-18, which present on Ubuntu 18.04.1 Mate as well

The Debian bug report further suggests the problem should be limited to the 32-bit edition.

In his message, https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=899338#25, Albarto Garcia mentions a workaround which permits Software-Boutique to function properly again.

The workaround is disabling the JIT by exporting the environment variable JavaScriptCoreUseJIT=0

Checked from the commandline by executing:

export JavaScriptCoreUseJIT=0
ubuntu-mate-welcome --boutique

and the Software-Boutique seemed to work properly again.

Alberta Garcia also mentions that he believes the bug has been fixed on Debian in the most recent webkit2gtk package. Yet, in case this is true, then this fix has not made its way into Ubuntu, yet.

So for the moment for me the workaround is still the way to go:
export JavaScriptCoreUseJIT=0
ubuntu-mate-welcome --boutique

And as I do not feel like executing this in the terminal every time, I have amended the appropriate .desktop file: $HOME/.local/share/applications/ubuntu-mate-welcome_software-boutique.desktop

Amended line:
Exec=env JavaScriptCoreUseJIT=0 BAMF_DESKTOP_FILE_HINT=/var/lib/snapd/desktop/applications/ubuntu-mate-welcome_software-boutique.desktop /snap/bin/ubuntu-mate-welcome.software-boutique %U

Note the "JavaScriptCoreUseJIT=0"

Applied the same to the file $HOME/.local/share/applications/ubuntu-mate-welcome_ubuntu-mate-welcome.desktop in order to make sure Software Boutique works when invoked from inside the Welcome Screen.

Exec=env JavaScriptCoreUseJIT=0 BAMF_DESKTOP_FILE_HINT=/var/lib/snapd/desktop/applications/ubuntu-mate-welcome_ubuntu-mate-welcome.desktop /snap/bin/ubuntu-mate-welcome %U

Hope the workaround will help others, too, and exhibit no negative side-effects.