Problem with libGL drivers when attempting to run Second Life viewers

Hello.

I'm a relative newcomer to Slackware (since September 2019). Mostly very satisfied with the distro, with the exception of a few issues. One concerns the libGL drivers when attempting to run ANY of the viewer software for Second Life virtual world. Using SlackBuild scripts, I successfully compiled and installed the native Second Life viewer, as well as Singularity, and Firestorm-opensim. All of these fail to run, with the same error messages:

libGL error: unable to load driver: i965_dri.so
libGL error: driver pointer missing
libGL error: failed to load driver: i965
libGL error: unable to load driver: swrast_dri.so
libGL error: failed to load driver: swrast
The program 'do-not-directly-run-firestorm-bin' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadValue (integer parameter out of range for operation)'.
(Details: serial 33 error_code 2 request_code 153 minor_code 3)

libGL error: unable to load driver: i965_dri.so
libGL error: driver pointer missing
libGL error: failed to load driver: i965
libGL error: unable to load driver: swrast_dri.so
libGL error: failed to load driver: swrast
The program 'do-not-directly-run-secondlife-bin' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadValue (integer parameter out of range for operation)'.
(Details: serial 33 error_code 2 request_code 153 minor_code 3)

Does anyone have a solution to this? In the meantime, I can still run Second Life on my Devuan distro which is available on a second drive of my dual-boot desktop.

Cheers