KeyError 'some_field_for_form_a' is not found in FormB during concurrent requests

[JacoBezuidenhout]

Hello everyone. I am posting this because I am out of ideas. I have tried to find the cause of this issue for the last 2 years.

Say I have 4 model admins:

TabbedAdminMixin, ModelAdmin
a: BasketAdmin
b: ConsumerAdmin

Normal Django ModelAdmin
c: RoleAdmin
d: BranchAdmin

It took me veeeery long to be able to find a way to re-create this error but as of yesterday, I can easily re-create it by using locust to simulate concurrent requests.

When I run locust with 5 concurrent users, each doing requests to /basket//change/ and /consumer//change/ I get a keyerror where render_tab_fieldsets_inlines want to create a, for example, BasketAdmin with fields from ConsumerAdmin's form and vice versa.

When I run the same locust file on /role//change/ and /branch//change/ (vanilla django modeladmins) I don't get keyerrors. This happend locally with runserver and in production with uwsgi.

Any help will be very much appreciated!