What does dotted line text bubble mean?

this window shows up on my imac.

around the "you don't agree" are images on my iphone. so they are not getting synch'd on the imac for some reason. the "you don't agree" is snch'd across devices. why there are dropouts, who knows, but the shadow knows.

I think what this means is that synch'd messages are not visible on the device that has the bubble.

i've been trying to fix it for months with apple tech support, but i think it's a bug that needs fixing, but since messages is a low priority, it doesn't get fixed