Further amendment based on review

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -622,8 +622,8 @@ namespace Discord.API
             Preconditions.GreaterThan(args.AfterUserId, 0, nameof(args.AfterUserId));
             options = RequestOptions.CreateOrClone(options);
 
-            var limit = args.Limit.GetValueOrDefault(DiscordConfig.MaxUserReactionsPerBatch);
-            var afterUserId = args.AfterUserId.GetValueOrDefault(0);
+            int limit = args.Limit.GetValueOrDefault(DiscordConfig.MaxUserReactionsPerBatch);
+            ulong afterUserId = args.AfterUserId.GetValueOrDefault(0);
 
             var ids = new BucketIds(channelId: channelId);
             Expression<Func<string>> endpoint = () => $"channels/{channelId}/messages/{messageId}/reactions/{emoji}?limit={limit}&after={afterUserId}";

src/Discord.Net.Rest/Entities/Messages/MessageHelper.cs

@@ -60,7 +60,7 @@ namespace Discord.Rest
                 async (info, ct) =>
                 {
                     var args = new GetReactionUsersParams();
-                    func(args);
+                    args.Limit = info.PageSize;
 
                     if (info.Position != null)
                         args.AfterUserId = info.Position.Value;
@@ -81,8 +81,8 @@ namespace Discord.Rest
                     info.Position = lastPage.Max(x => x.Id);
                     return true;
                 },
-                start: arguments.AfterUserId.Value,
-                count: arguments.Limit.Value
+                start: arguments.AfterUserId.IsSpecified ? arguments.AfterUserId.Value : (ulong?)null,
+                count: arguments.Limit.GetValueOrDefault(DiscordConfig.MaxUserReactionsPerBatch)
             );
 
         }