This seems to be very similar to what is being discussed in interProcess - Permission denied when creating named_mutex. There is also: https://bugs.launchpad.net/snapcraft/+bug/1577514/comments/2. Perhaps LD_PRELOAD is getting cleared along the way (Shared memory in /dev/shm rewriting).
As mentioned earlier, nwjs uses the chromium content api. Oxide was adjusted to account for this: https://git.launchpad.net/oxide/commit/?id=9bbf87e80b49e6abcc9419f142655a4ce2fc0638. Ideally nwjs would be updated to include a similar patch. Would they be amenable to that? (FTR, this would also be a nice improvement for electron apps).
As mentioned, we can hack up browser-support for this, but we should only do that as a last resort.