Asymmetric routing of management traffic

[userfw]

I am experiencing some strange issues with management traffic (https and ssh) over a multi-WAN configuration: TCP SYN goes to one of the interfaces whose address I'm trying to connect to and return traffic exits from the other interface with higher gateway priority hence chosen as default, I thought that this wasn't supposed to happen with reply-to.

There aren't any PBRs or static routes that can influence this choice. I have another opnsense instance elsewhere configured almost identically that is not exhibiting this behaviour.

Any hints at where to look?