Q:

Working Magento 2.1 site broken on new server

I have built a new store based on Magento 2.1.6.  It is working fine on Host 1. 
I am in the process of moving this store from host 1 to host 2. 
I used RSYNC to copy all the file system of the working site to the new server, then used RSYNC to check for any file inconsistencies between the two servers.  Other than owner and group differences between servers, everything appears to be fine. 
On Host 2, the admin is accessible, and working fine.  However, the front end has broken with an error as follows:
1 exception(s):
Exception #0 (Exception): Warning: simplexml_load_string(): namespace error : Namespace prefix xmlns123 for xsi on handle is not defined in /var/www/vhosts/mysite/htdocs/vendor/magento/framework/View/Model/Layout/Merge.php on line 493

On host 1, the site was running on Apache, while on host 2, we are using NginX. The rest is much the same (PHP 7 and MySQL, although using the MariaDB engine on Host 2). 
Nothing appears to be getting logged regarding this error in the server logs, or the magento logs. 
The site is in "development" mode, but I have flushed and cleaned the cache, etc, but something is busted somewhere, and I am unsure where due to a lack of available information? 
Any thoughts anyone? 

A:

It seems like there is some error in your xml file.   Well as magento has sooo many xml files and its very hard to do trial and error  on your modules by disabling them one by one and checking if your site loads. 
You may use sublime if you have the same copy on your local. 

Open project in sublime , you may simply drop the magento root folder in sublime and follow these steps:

1) right click on your project in sublime and select find in folder
2) in find text box enter xmlns123 and hit enter

This will search for text in whole magento and this will take some time. 
To narrow the search area you may search in vendor directory or in magento app directory .  If you find the file just remove that 123 from xmlns123 

