We are in the process of migrating our Umbraco installation from 7.2.4 to 7.3.5. After upgrade and while testing front-end server and back-end server scenarios, we observed that front-end server is missing some updates which were made on the back-end (master) server.

Once front-end misses the update, it never applies that update. In the log files, we are seeing messages like 'file is locked as being used by another process'. This may be because there were users accessing the application and 'umbraco.config' is in use.

We looked into Umbraco source code and found below code. Below code in the class seems to ignore any updates resulting in exceptions. Is there any way to retry failed updates?

Class: DatabaseServerMessenger

Method name: ProcessDatabaseInstructions()

// execute remote instructions & update lastId
            try
            {
                NotifyRefreshers(jsonA);
                lastId = dto.Id;
            }
            catch (Exception ex)
            {
                _logger.Error<DatabaseServerMessenger>(
                    string.Format("DISTRIBUTED CACHE IS NOT UPDATED. Failed to execute instructions ({0}: \"{1}\"). Instruction is being skipped/ignored", dto.Id, dto.Instructions), ex);

                //we cannot throw here because this invalid instruction will just keep getting processed over and over and errors
                // will be thrown over and over. The only thing we can do is ignore and move on.
                lastId = dto.Id;
            }

Is there any other solution to fix this issue?

Thank you for your help!