Solaris crashes with SOP volumes

**Describe the bug**
While working in Solaris, I experience random crashes (particularly when I exit the Arnold delegate)

**To Reproduce**
Steps to reproduce the behavior:
1. Create a SOP vdb
2. SOP Import it into /stage
3. Start an Arnold render
4. Switch back to SOPs, or something which will force the delegate to be stopped

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Used Software Versions**
- Arnold: [e.g. 5.4.0.2]
- USD: [e.g. 0.19.11]
- Compiler: [e.g. GCC 4.8.5]
- OS: [e.g. MacOS 10.15]
- Any 3rd-party app: [e.g. Katana-3.2]

**Additional context**
Add any other context about the problem here.

Start by reproducing the Solaris crash with the listed SOP VDB, SOP Import, Arnold render, and delegate-stop steps. Record the Arnold, USD, compiler, OS, and third-party application versions requested in the issue, then trace the Arnold delegate shutdown path; done means switching away from SOPs no longer crashes.

Written by the indexing model from the issue text.