Where does it sometimes work? Because it most certainly isn’t. Ike probably receives attack/defense from something else, say from a tactics, hone/fortify skill. Or maybe a drive, because Fjorm would drive his attack by 3 points when she’s within 2 spaces of him. (and if she has the drive defense seal, then she’d also give him +3 defense). Ike could be getting these buffs from your other team members too.
Bonds only affect the unit with the skill/seal is on and are active when any teammate is immediately next to them.