If you intermittently see race reports where one stack is missing with a failed to restore the stack message, this can indicate that a suppression is partially covering the race you are seeing.
Any race where only one of the two stacks is matched by a runtime suppression will show up if that particular stack fails to symbolize for some reason. The usual solution is to search the suppressions for potential candidates and disable them temporarily to check if your race report now becomes mostly consistent.
However, there are other reasons for broken TSan stacks, in particular if they are not intermittent. See also the history_size parameter in the TSan flags.
https://firefox-source-docs.mozilla.org/tools/sanitizer/tsan.html#intermittent-broken-stacks