Dual sim: Sending messages always changes lines

Hi folks,

raising this thread because all similars are outdated and were not helpful.

I have an issue sending SMS/ iMessage from my second line in Dual SIM mode. First SIM (Private) is a classic SIM card, second SIM (Business) is an eSIM.

Everytime i try to send a message from my Business line, the conversation settings are automatically switched to "Private" setting and all my messages will be sent from Private line. Receiving messages on my business line works perfectly, which makes it especially awkward when they receive my response coming from my private line. I recorded a small test case in a conversation with myself to maybe help clarifying the issue.

Appreciate any help.