You can enable wordpress debugging to get more detailed error messages. Start here:
https://codex.www.ads-software.com/Debugging_in_WordPress
The two arguments can be added near the top of the file and commented out when you are done troubleshooting, for future use.
For example from my wp_config.php (I just use the edit file in my hosting’s file manager to change this).
/**
* For developers: WordPress debugging mode.
*
* Change this to true to enable the display of notices during development.
* It is strongly recommended that plugin and theme developers use WP_DEBUG
* in their development environments.
*
* For information on other constants that can be used for debugging,
* visit the Codex.
*
* @link https://codex.www.ads-software.com/Debugging_in_WordPress
*/
define('WP_DEBUG', true);
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );
If you need to correct something at the configuration or database layer related to the import, after looking at what the debugging is telling you, the following can help.
(1) Are you importing into a multi-site or multi-network configured wordpress (which plugin are you using)?
(2) Is only the newly imported site failing, your statement of “different site on the same host”… is the site you were working on “yesterday” still working (can you access wp-admin/ on the site from yesterday)
(3) Do you have access to your underlying DB with phpDBadmin or something like that?
Back the DB up before starting, make sure you understand how to recover the DB if you need. Make changes one at a time and verify impact so you can go back and undo if necessary.
First a primer on the “first site” DB. The additional “sites” end up with a number in front of these table names. This is a good quick reference to the overall DB layout
https://codex.www.ads-software.com/Database_Description
There is a good database writeup of what the running wordpress instance uses to map the sites and their information in the DB.
YOU WILL NOT FOLLOW THIS EXACTLY, this is more for education on how things are laid out. You will need to verify what the wp_site, wp_options, wp_blog, etc. and then understand which ##_wp_blogs the site is mapping too.
https://wpengine.com/support/how-to-change-a-multi-site-primary-domain/
MAKE A BACKUP BEFORE CHANGING ANYTHING IN THE DB (yep I repeated it, here comes the rest…). Make changes one at a time and test so you understand the change and impact… back out before doing a bunch of stuff experimenting.
In the past I’ve had to update in the DB to correct URL changes that might have come in from the import… or if importing but multi-site/multi-network as a plugin is not enabled…
If you are importing plugins… perhaps version issue?
Make sure you are backing up before each import attempt…
