Workaround for bug in BlockListPropertyEditor https://github.com/umbraco/Umbraco-CMS/issues/10910

BlockListPropertyEditorTempFix.cs

using System;
using Umbraco.Core;
using Umbraco.Core.Composing;
using Umbraco.Core.Configuration;
using Umbraco.Core.Logging;
using Umbraco.Core.PropertyEditors;
using Umbraco.Core.Runtime;
using Umbraco.Core.Services;
using Umbraco.Web.PropertyEditors;

namespace Umbraco.Web.PropertyEditors
{
    [ComposeAfter(typeof(CoreInitialComposer))]
    public class BlockListPropertyEditorTempFixComposer : IUserComposer
    {
        public void Compose(Composition composition)
        {
            // bug was introduced in 8.15, doesn't affect earlier versions
            // https://github.com/umbraco/Umbraco-CMS/issues/10910
            if (UmbracoVersion.Current <= new Version(8, 15)) 
                return; 

            // bug was fixed in 8.15.3
            if (UmbracoVersion.Current >= new Version(8, 15, 3))
                return;

            // exclude the BlockListPropertyEditor with the bug
            composition.DataEditors().Exclude<BlockListPropertyEditor>();

            // and re-register it with a workaround
            composition.DataEditors().Add<BlockListPropertyEditorTempFix>();
        }
    }

    [DataEditor(
        Constants.PropertyEditors.Aliases.BlockList,
        "Block List",
        "blocklist",
        ValueType = ValueTypes.Json,
        Group = Constants.PropertyEditors.Groups.Lists,
        Icon = "icon-thumbnail-list")]
    [HideFromTypeFinder]
    public class BlockListPropertyEditorTempFix : BlockListPropertyEditor, IDataEditor
    {
        public BlockListPropertyEditorTempFix(ILogger logger, Lazy<PropertyEditorCollection> propertyEditors, IDataTypeService dataTypeService, IContentTypeService contentTypeService, ILocalizedTextService localizedTextService) 
            : base(logger, propertyEditors, dataTypeService, contentTypeService, localizedTextService)
        {

        }

        IDataValueEditor IDataEditor.GetValueEditor()
        {
            // base method caches the editor, but inadvertently caches doctypes too. 
            // call CreateValueEditor directly to prevent the cached _reusableEditor from being used
            // https://github.com/umbraco/Umbraco-CMS/issues/10910
            return CreateValueEditor();
        }
    }
}