Replace the Sitecore 10.2.1 cumulative hotfix implementation with what was originally provided in 10.2.0.

ResolveUser.cs

using Microsoft.AspNet.Identity;
using Sitecore.Diagnostics;
using Sitecore.Owin.Authentication.Extensions;
using Sitecore.Owin.Authentication.Pipelines.CookieAuthentication.SignIn;
using Sitecore.Owin.Authentication.Services;
using Sitecore.Security.Accounts;
using System.Security.Claims;

namespace Scms.Feature.Security.Pipelines.CookieAuthentication.SignIn
{
    public class ResolveUser : SignInProcessor
    {
        protected ApplicationUserFactory ApplicationUserFactory
        {
            get;
        }

        protected UserFactory UserFactory
        {
            get;
        }

        public ResolveUser(ApplicationUserFactory applicationUserFactory, UserFactory userFactory)
        {
            Assert.ArgumentNotNull(applicationUserFactory, "applicationUserFactory");
            Assert.ArgumentNotNull(userFactory, "userFactory");
            this.ApplicationUserFactory = applicationUserFactory;
            this.UserFactory = userFactory;
        }

        public override void Process(SignInArgs args)
        {
            string name;
            Assert.ArgumentNotNull(args, "args");
            ClaimsIdentity identity = args.Context.Identity;
            if (identity != null)
            {
                name = identity.Name;
            }
            else
            {
                name = null;
            }
            string str = name;
            if (!string.IsNullOrEmpty(str) && args.Context.OwinContext.GetUserManager().FindByName(str) != null)
            {
                User user = this.UserFactory.CreateUser(new ClaimsPrincipal(args.Context.Identity));
                args.User = this.ApplicationUserFactory.CreateUser(user);
            }
            if (args.User == null)
            {
                args.Success = false;
                args.AbortPipeline();
            }
        }
    }
}

Scms.Feature.Security.config

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/" xmlns:set="http://www.sitecore.net/xmlconfig/set/" xmlns:role="http://www.sitecore.net/xmlconfig/role/">
  <sitecore role:require="Standalone or ContentManagement">
    <pipelines>
      <owin.cookieAuthentication.signIn>
        <processor patch:instead="processor[@type='Sitecore.Owin.Authentication.Pipelines.CookieAuthentication.SignIn.ResolveUser, Sitecore.Owin.Authentication']" type="Scms.Feature.Security.Pipelines.CookieAuthentication.SignIn.ResolveUser,Scms.Feature" resolve="true"/>
      </owin.cookieAuthentication.signIn>
    </pipelines>
  </sitecore>
</configuration>