I'm now using the latest firmware version from Ailunce for the Retevis RT73. The firmware file is "Retevis_RT73_20210203.bin" which seems to work well. I can now load all my world-wide Contacts and they display perfectly. The radio seems to be stable (so far).
I'm not sure why there is a delay in releasing a similar firmware update for the Kydera CDR-300UV.
Here is the Ailunce revision list:
FW update date: 2021-02-03 1. Fix the problem that Ham contacts are being loaded ONLY in blocks of 65536 items each. If you load less than 65536 items, nothing will be loaded; If you load more than 65536 items, only first 65536 items will be loaded; if you load more than 131072 items, only first 131072 items will be loaded. 2. Add “Dual Watch on/off” in preset button.
Software update date: 2021-1-28 Version：9.1.170 1. Revised the preset button explanation to “ Radio Enable” “Radio Check” “Radio Disable” ”Promiscuous” . 2. Add ”Dual Watch on/off”.