I know warnings are .... warnings.

But do these warnings/messages give you any pause?

The following error occurred: 
E_DEPRECATED: explode(): Passing null to parameter #2 ($string) of type string is deprecated 
File: /var/www/vhosts/example.com/system/user/config/config.php
Line: 26
The following error occurred: 
E_DEPRECATED: explode(): Passing null to parameter #2 ($string) of type string is deprecated 
File: /var/www/vhosts/example.com/system/user/config/config.php
Line: 26
The following error occurred: 
E_WARNING: session_set_cookie_params(): Session cookie parameters cannot be changed after headers have already been sent 
File: /var/www/vhosts/example.com/system/ee/legacy/libraries/Core.php
Line: 165
Starting: Upholstery Parent… 
The following error occurred: 
E_WARNING: Cannot modify header information - headers already sent by (output started at /var/www/vhosts/example.com/system/ee/ExpressionEngine/Boot/boot.common.php:727) 
File: /var/www/vhosts/example.com/system/ee/legacy/core/Input.php
Line: 266
The following error occurred: 
E_WARNING: mkdir(): File exists 
File: /var/www/vhosts/example.com/system/user/addons/speedy/Service/Drivers/FilesystemDriver.php
Line: 133
The following error occurred: 
E_WARNING: mkdir(): File exists 
File: /var/www/vhosts/example.com/system/user/addons/speedy/Service/Drivers/FilesystemDriver.php
Line: 133
The following error occurred: 
E_WARNING: unlink(/var/www/vhosts/example.com/system/user/cache/speedy/default_site/local/furniture/stressless-view-office/stressless-view-office-barstool_images_second): No such file or directory 
File: /var/www/vhosts/example.com/system/user/addons/speedy/Service/Drivers/FilesystemDriver.php
Line: 37
The following error occurred: 
E_WARNING: unlink(/var/www/vhosts/example.com/system/user/cache/speedy/default_site/local/furniture/stressless-view-office/stressless-view-office-barstool_images_third): No such file or directory 
File: /var/www/vhosts/example.com/system/user/addons/speedy/Service/Drivers/FilesystemDriver.php
Line: 37
The following error occurred: 
E_WARNING: unlink(/var/www/vhosts/example.com/system/user/cache/speedy/default_site/local/furniture/stressless-view-office/stressless-view-office-product-options): No such file or directory 
File: /var/www/vhosts/example.com/system/user/addons/speedy/Service/Drivers/FilesystemDriver.php
Line: 37

My speedy rules probably trigger on entry save with this import. Sometimes the imports get stuck, and I have to coax/re-run them.

I don’t see this as a bug… and in Centos/Plesk, the loud warnings weren’t a thing in PHP7, so I’m on the hunt in those forums to reduce the warning level.