Disappearing semaphore array

I've run into an issue with a semaphore array disappearing from the system while the app is running. I can't find any details in the logs about what would cause it, but it started happening pretty much as we moved from ubuntu 14.04 to 18.04. There are no other changes that I could see that would be related here.

The system is running with ruby 2.5.5. The exception we get is:

Semian::SyscallError: semop() failed, errno: 22 (Invalid argument)

File .../vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/protected_resource.rb line 50 in acquire
File .../vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/protected_resource.rb line 50 in acquire_bulkhead
File .../vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/protected_resource.rb line 24 in block in acquire
File .../vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/protected_resource.rb line 38 in block in acquire_circuit_breaker
File .../vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/circuit_breaker.rb line 141 in maybe_with_half_open_resource_timeout
File .../vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/circuit_breaker.rb line 30 in acquire
File .../vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/protected_resource.rb line 37 in acquire_circuit_breaker
File .../vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/protected_resource.rb line 23 in acquire
File .../vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/adapter.rb line 34 in acquire_semian_resource
File .../vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/net_http.rb line 83 in connect

This is with the latest released semian.

The issue starts occurring a number of hours after the deployment, without any obvious pattern of traffic.

I tracked the call down to:

10574.300 ( 0.015 ms): ruby/21041 semtimedop(semid: 131072, tsops: 0x7ffff92379c2, nsops: 1, timeout: 0x7ffff9237aa8) = -1 EINVAL Invalid argument

where the semid: 131072 doesn't exist on the system (normally we have 2 semaphore arrays, but this system had only 1). This was validated using ipcs -s.

Please let me know if there's any more debugging information I can provide.

Start at vendor/bundle/ruby/2.5.0/gems/semian-0.8.8/lib/semian/protected_resource.rb line 50, where acquire calls semtimedop, and compare the failing semid with ipcs -s. Investigate the Ubuntu 14.04-to-18.04 environment and semaphore lifecycle; done means identifying a reproducible cause or documenting the missing diagnostic needed to resolve the disappearance.