Notices /warnings are nothing to worry about. it has nothing to do with the actual functionality. but if you are saying this i will have a look on this please share page url & credentials in a private reply.
What are PHP Notices?
PHP notices are the least important. As stated on the official PHP website, you will see PHP notices when:
the script encountered something that could indicate an error, but could also happen in the normal course of running a script.
Refer: https://www.ostraining.com/blog/wordpress/warnings/.
Export/import tutorial:
https://wplms.io/support/knowledge-base/wplms-site-import-and-export/