Spurious build failure related to MicroC (?)

I am observing occasional build failures for AutoCorrode in the CI:

```
AutoCorrode FAILED (see also "isabelle build_log -H Error AutoCorrode")
*** Failed to load theory "AutoCorrode.AutoCorrode" (unresolved "Micro_C_Examples.C_Union_Examples")
*** micro_c_translate: missing struct field accessor constant: c_U_i
*** At command "micro_c_translate" (line 132 of "/__w/AutoCorrode/AutoCorrode/Micro_C_Examples/C_Union_Examples.thy")
Presentation in "/github/home/.isabelle/browser_info"
```

**Task:** Understand and fix this so that CI reliably succeeds.