Get them to send you their linux binary. <---- very important
If you can't run it due to shared libraries missing, it will tell you what library versions it wants so you can duplicate the same environment.
Then repeat the rpc commands using their binary on your wallet. It should break the same way, and then you can witness what they are telling you.
Once that happens, you can re-build your own wallet using those same exact library versions and see if it crashes using your binary. If it does, then you have source code now to troubleshoot the problem.
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