Hello,
Thank you for contacting Rank Math, and sorry for any inconvenience caused.
To fix the sitemap issue, please follow these steps:
1. Flush the Sitemap cache by following this video screencast:
https://i.rankmath.com/pipRDp
2. Exclude the Sitemap files of the Rank Math plugin in your caching plugin. The cache could be via a plugin or from the server. For plugins or Cloudflare, please follow this article:
https://rankmath.com/kb/exclude-sitemaps-from-caching/
That should fix the issue.
Regarding the notice, where are you seeing the notice?
Can you please share a screenshot using https://imgbb.com/?
Also, please share the error log with us.
Having an error log will help us determine what is causing the issue on your website.
You can follow this guide to enable debugging in WordPress
https://wordpress.org/support/article/debugging-in-wordpress/ or you can get in touch with your web host, they will help you locate the log file.
We really look forward to helping you.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.