How can we escalate issues to second or third line support and at last to the SP development team?

[Andre @ NL Salomons]

In some occasions first line support from Office365 is not enough. You get first line support that is not able to forward bugs or issues in SPO to the development team as last resort! Or escalate to the SPO development team

In cases we find issues/bugs that they cannot escalate to the SharePoint team. 

There are situations that by design consistencies have been created. In that case we want to forward suggestions to the development team ...

HOW? Who can you help us with this?

[#2]

How are you submitting issues? Calling in, from M365 Admin center, from SharePoint Online Central admin, etc?

Have you tried the feedback on the MS documentation pages? There is a link to the git hub there.

Have you contacted your MS CSAM and asked them to escalate?

[#3]

See here:
https://docs.microsoft.com/en-us/sharepoint/dev/support-feedback