You don't think it's enough ground plane? It's got 24 feet of metal behind it haha
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The way you have it mounted may be the issue.
With the ground plane going down towards the ground, it's not really a suitable ground plane for a vertical antenna. The ground needs to be relatively horizontal.
While you can make an install like that work, it's going to impact the characteristic impedance of the install.
I wouldn't be surprised if the SWR is high, but this could easily be a number of issues combined:
High SWR due to mount.
Coax damage. Could be pinched however you ran it into the radio.
Could be the antenna is not trimmed correctly.
Could be a bad antenna
Could be a bad mount.
Could be a improperly adjusted SWR warning indicator, as was mentioned above.
Using a reliable SWR meter will tell you a lot. Relying on SWR "warning lights" is not a good indicator of the issue (if there is one).