Update on sitemap error

Hello, I installed your plugin and did some tests but I found errors on the dates.
I have posts since 2005, I used your plugin to update all posts (17843 posts) and gives me a message confirming the update but when I open the sitemap my articles still result with date -001-11-30 01 : 00 +01: 00
When I open an article manually and click on “update” then the update date is taken and the date on the sitemap is also corrected otherwise not.
Is this error normal?
Thank you!