Custom MembershipProvider not working after hotfix for .net

Error - There is no configuration for data provider with the name of "myprovider" for "Telerik.Sitefinity.Security.UserManager" manager. Please check the spelling of the name and whether such configuration exists.

I've just patched my app to 8.1.5830 to get around the .net 4.7 issue.  Whilst Sitefinity now starts up and I can get in to the back-end I can't log in to to our front-end pages which use a custom membership provider to log in via another system.

We've been happily using a simple custom provider that is added in web.config (we've not had need to go down the route of inheriting from MembershipDataProvider  hence we can re-use the simple providers that we use in some other web apps.

I can only presume that the hotfix has changed something which means Sitefinity no longer sees the membership provider registered in web.config and is expecting to find a custom provider entry in securityconfig.config instead.  

As we've got multiple providers that are all actively used within other apps I'd prefer to not have to write a new set of providers using MembershipDataProvider as the base if possible.

Update from Progress support - an edit to the web.config appears to resolve the issue.

See hotfix article - knowledgebase.progress.com/.../custom-membership-provider-dropdown-does-not-appear

In case that URL is changed in future the TLDR is:

Remove the default provider in the web.config and set as defaultProvider the custom provider.

In my case I can confirm that I still get the option to use the default provide in the backend (which is what I want) but my custom provider once again works for logging in to the front-end site.