We are running Aspace 2.8.1 on Oracle Linux 6.10.

If I do Create>Event, link the event to an archival object and add an agent to the event, I'm able to create an event without issue.

However when I search for a resource and create an event for an associated archival object and add an agent, I receive a generic error upon trying to create the event. Here's what I'm seeing in the archivesspace.out log when this happens:

[2021-03-31T14:20:14.389878 #21314] INFO -- : Started GET "/resolve/edit?uri=%2Frepositories%2F2%2Farchival_objects%2F25585" for 153.104.85.204 at 2021-03-31 14:20:14 -0400
I, [2021-03-31T14:20:14.392270 #21314] INFO -- : Processing by ResolverController#resolve_edit as HTML
I, [2021-03-31T14:20:14.392371 #21314] INFO -- : Parameters: {"uri"=>"/repositories/2/archival_objects/25585"}
I, [2021-03-31T14:20:14.418297 #21314] INFO -- : Completed 500 Internal Server Error in 24ms
F, [2021-03-31T14:20:14.425519 #21314] FATAL -- :
F, [2021-03-31T14:20:14.425852 #21314] FATAL -- : NoMethodError (undefined method []' for nil:NilClass): F, [2021-03-31T14:20:14.426016 #21314] FATAL -- : F, [2021-03-31T14:20:14.426199 #21314] FATAL -- : app/models/resolver.rb:9:in initialize'
app/controllers/resolver_controller.rb:8:in resolve_edit' I, [2021-03-31T14:20:14.561130 #21314] INFO -- : Started GET "/favicon.ico" for 153.104.85.204 at 2021-03-31 14:20:14 -0400 F, [2021-03-31T14:20:14.563305 #21314] FATAL -- : F, [2021-03-31T14:20:14.563497 #21314] FATAL -- : ActionController::RoutingError (No route matches [GET] "/favicon.ico"): F, [2021-03-31T14:20:14.563671 #21314] FATAL -- : F, [2021-03-31T14:20:14.563841 #21314] FATAL -- : actionpack (5.2.4.4) lib/action_dispatch/middleware/debug_exceptions.rb:65:in call'

Here's a video showing how to reproduce the issue:
https://vimeo.com/531443028

Oddly, after receiving the error the events show as if they have passed but in the resource record the events aren't linked:
https://i.imgur.com/8vuwo6a.png