You’re welcome.
It does sound like something isn’t grounded correctly. Weak or no RX can be due to an antenna ground issue, or the mic pins may be slightly out of alignment.
I’m not sure of the science behind it as I’m not a mic expert, but your typical radio (like yours) doesn’t have an “active” mic, but the connector still makes a difference. That is, it doesn’t draw power from the radio via the cord. [Some do use mic cords to get power to an active mic, such as certain Magnum brand “export” radios.] Even though your Uniden has a normal mic, believe it or not the cord becomes part of the circuit and you won’t get any RX audio if the mic isn’t fit in carefully. Again, I’m not exactly sure why, but that’s the case with many radios. I could start speculating but you’d fall asleep.
Edit to add: I can’t see your mount too well. Is it all metal on metal, no paint? Has to be, even if only in one spot (not ideal but at least it’d work). And the bumper should be mounted to metal as well. Your ground is traveling through that.
Did you calibrate your SWR meter first?