This was my thinking until I read this just a moment ago:
"CHIRP reads the firmware version of the radio to compare it with the firmware version of the currently selected tab. This is because there are different Aux memory layouts in these radios. If you upload an image into a different radio than it was downloaded from, you run the risk of uploading an incompatible Aux memory layout that will cause undesired behavior (squelch won't open, radio won't scan, etc). So if the firmware versions don't exactly match, only small part of the Aux memory is uploaded.
Because of this, you should never directly upload an image from one radio into another radio even if the firmware versions are exactly the same. You should load a saved image from the source radio (or download from the source radio). Next you should download from the target radio to create a compatible tab. Copy-and-paste the channels from the source radio tab to the target radio tab. Finally upload the target radio tab back into the target radio. This completely prevents corruption of the Aux memory area (along with its undesired behavior) by overwriting it with incompatible data from another radio."
See note 11 from Brogdan N. at https://chirp.danplanet.com/issues/10505