Happens to me allot at random recently on variables that are being referenced by many Blueprints. Which is sad as a lot of things rely on that variable so game breaks are a pain. Oddly enough if you are not using replication I found a way around it using BP Communication vs direct calls. Its a pain ill agree. i usually have to delete the node and put in a new one to get it working again as long as you don’t change the name or compile after deleting the variable to replace it all other referencing blueprints should pick it right back up without a problem.
also i find it happens more when It is a custom variable on an Spawn node.
I put this up there with reroute nodes inheriting a variable type and refusing to or breaking connections if you change the variable type … like why ? it should just change but no you have to delete all of them and place new ones (Pull Hair)