problem still persists.

@jb could you add more information about your system?

What DE or WM are you using, maybe other relevant information since I did not see this sort of crash on any of my systems.

My system is up to date.
I use XFCE desktop env.
The problem started to occur with the last two Opera versions (Arch repo).
I removed Opera from pacman database and cleaned it, then reinstalled Opera from repo.

$ pacman -Q |grep opera
opera 48.0.2685.35-1

$ rm -rf .cache/opera/
$ rm -rf .config/opera/

Started Opera.

$ coredumpctl
Mon 2017-10-09 15:55:16 CEST 21764 1000 1000 6 present /usr/lib/opera/opera_autoupdate

$ journalctl
...
Oct 09 15:55:15 myhost systemd[1]: Started Process Core Dump (PID 21793/UID 0).
Oct 09 15:55:16 myhost systemd-coredump[21794]: Process 21764 (opera_autoupdat) of user 1000 dumped core.

Stack trace of thread 21764:
#0 0x00007ff632e7b8a0 raise (libc.so.6)
#1 0x00007ff632e7cf09 abort (libc.so.6)
#2 0x00000000004cf382 n/a (opera_autoupdate)
#3 0x00000000004a22b3 n/a (opera_autoupdate)
#4 0x00000000004f55aa n/a (opera_autoupdate)
#5 0x00000000004f5809 n/a (opera_autoupdate)
#6 0x00000000004ecc5a n/a (opera_autoupdate)
#7 0x00000000004e988d n/a (opera_autoupdate)
#8 0x00000000004e9969 n/a (opera_autoupdate)
#9 0x000000000040c06e n/a (opera_autoupdate)
#10 0x000000000040c0f9 n/a (opera_autoupdate)
#11 0x0000000000409723 _start (opera_autoupdate)
#12 0x00000000004093c1 _start (opera_autoupdate)
#13 0x00007ff632e67f6a __libc_start_main (libc.so.6)
#14 0x0000000000409099 _start (opera_autoupdate)

$ $ ps -aux |grep -i opera
jb 21634 0.8 3.0 1065392 61468 tty1 Sl 15:55 0:05 /usr/lib/opera/opera
jb 21636 0.0 0.0 6456 792 tty1 S 15:55 0:00 /usr/lib/opera/opera_sandbox /usr/lib/opera/opera --type=zygote
jb 21637 0.0 0.7 423460 14708 tty1 S 15:55 0:00 /usr/lib/opera/opera --type=zygote
jb 21639 0.0 0.2 423460 5196 tty1 S 15:55 0:00 /usr/lib/opera/opera --type=zygote
jb 21671 0.2 3.4 713824 70508 tty1 Sl 15:55 0:01 /usr/lib/opera/opera --type=gpu-process ...
jb 21698 0.0 1.7 788300 36404 tty1 Sl 15:55 0:00 /usr/lib/opera/opera --type=renderer ...
jb 21738 0.0 0.3 484416 8008 tty1 S 15:55 0:00 /usr/lib/opera/opera --type=gpu-broker
jb 21746 0.6 3.0 828396 62456 tty1 Sl 15:55 0:03 /usr/lib/opera/opera --type=renderer ...
jb 21753 0.0 1.3 765776 26640 tty1 Sl 15:55 0:00 /usr/lib/opera/opera --type=renderer ...
jb 21758 9.1 3.4 839248 71268 tty1 Sl 15:55 0:52 /usr/lib/opera/opera --type=renderer ...

$ ldd /usr/lib/opera/opera_autoupdate
linux-vdso.so.1 (0x00007fff25f81000)
libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007f8324a20000)
libcurl.so.4 => /usr/lib/libcurl.so.4 (0x00007f832479f000)
libc.so.6 => /usr/lib/libc.so.6 (0x00007f83243e8000)
libm.so.6 => /usr/lib/libm.so.6 (0x00007f832409c000)
libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x00007f8323e85000)
libdl.so.2 => /usr/lib/libdl.so.2 (0x00007f8323c81000)
libglib-2.0.so.0 => /usr/lib/libglib-2.0.so.0 (0x00007f8323962000)
/lib64/ld-linux-x86-64.so.2 => /usr/lib64/ld-linux-x86-64.so.2 (0x00007f8324c3e000)
libnghttp2.so.14 => /usr/lib/libnghttp2.so.14 (0x00007f832373c000)
libssh2.so.1 => /usr/lib/libssh2.so.1 (0x00007f832350e000)
libpsl.so.5 => /usr/lib/libpsl.so.5 (0x00007f8323300000)
libssl.so.1.1 => /usr/lib/libssl.so.1.1 (0x00007f8323096000)
libcrypto.so.1.1 => /usr/lib/libcrypto.so.1.1 (0x00007f8322c16000)
libgssapi_krb5.so.2 => /usr/lib/libgssapi_krb5.so.2 (0x00007f83229c9000)
libkrb5.so.3 => /usr/lib/libkrb5.so.3 (0x00007f83226e3000)
libk5crypto.so.3 => /usr/lib/libk5crypto.so.3 (0x00007f83224b0000)
libcom_err.so.2 => /usr/lib/libcom_err.so.2 (0x00007f83222ac000)
libz.so.1 => /usr/lib/libz.so.1 (0x00007f8322095000)
libpcre.so.1 => /usr/lib/libpcre.so.1 (0x00007f8321e22000)
libicuuc.so.59 => /usr/lib/libicuuc.so.59 (0x00007f8321a72000)
libkrb5support.so.0 => /usr/lib/libkrb5support.so.0 (0x00007f8321865000)
libkeyutils.so.1 => /usr/lib/libkeyutils.so.1 (0x00007f8321661000)
libresolv.so.2 => /usr/lib/libresolv.so.2 (0x00007f832144a000)
libicudata.so.59 => /usr/lib/libicudata.so.59 (0x00007f831f937000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00007f831f5b0000)
$

When I start Opera from terminal cmd line, this happens (but not every time ...):
$ opera
[22900:22900:1009/170437.409881:161568845705:FATAL:interface_endpoint_client.cc(173)] Check failed: task_runner_->RunsTasksInCurrentSequence().
#0 0x0000004cf3d7 <unknown>
#1 0x0000004a1df1 <unknown>
#2 0x0000004f55aa <unknown>
#3 0x0000004f5809 <unknown>
#4 0x0000004ecc5a <unknown>
#5 0x0000004e988d <unknown>
#6 0x0000004e9969 <unknown>
#7 0x00000040c06e <unknown>
#8 0x00000040c0f9 <unknown>
#9 0x000000409723 <unknown>
#10 0x0000004093c1 <unknown>
#11 0x7fb5c7f82f6a __libc_start_main
#12 0x000000409099 <unknown>

I started Opera like below and it gave me two different errors:

$ opera %U
[1009/165718.216191:ERROR:CONSOLE(284)] "Uncaught (in promise) ReferenceError: StartPageConfigElement is not defined", source: chrome://startpage/default_start_page_view.js (284)

$ opera %U
[23090:23090:1009/170930.592091:161862027914:FATAL:interface_endpoint_client.cc(173)] Check failed: task_runner_->RunsTasksInCurrentSequence().
#0 0x0000004cf3d7 <unknown>
#1 0x0000004a1df1 <unknown>
#2 0x0000004f55aa <unknown>
#3 0x0000004f5809 <unknown>
#4 0x0000004ecc5a <unknown>
#5 0x0000004e988d <unknown>
#6 0x0000004e9969 <unknown>
#7 0x00000040c06e <unknown>
#8 0x00000040c0f9 <unknown>
#9 0x000000409723 <unknown>
#10 0x0000004093c1 <unknown>
#11 0x7fba2309af6a __libc_start_main
#12 0x000000409099 <unknown>
$