I’m mostly thinking out loud here.
I have an Icom 9700 connected to a set of egg beater antennas. The other day I noticed high SWR on 70 cm, so I broke out the dummy load and tested the patch cable running from the radio to the wall panel (along with the barrel connector on the wall panel). SWR was fine there. Then I took the outdoor feedline off the antenna and tested it there. Everything seems fine there too. Plugged it back into the antenna and the high SWR returned.
Seems the antenna is the problem, but I’m not sure how to fix it. The other egg beater is doing fine.
Well, antennas are pretty simple physical devices so a close visual inspection is the next step, looking for damage to insulators and spacers, etc
Eggbeater antennas also usually have a bit of phasing coax that by necessity sits out in the weather between the connections to the two elements, probably best to eyeball that too.