Unfortunately some MULTI-Module manufacturers have not followed the published open source schematic when designing and manufacturing their modules.
The most serious problem is where some manufacturers have used the incorrect microprocessor (MCU) in the module (even though they may advertise it as having the correct one).
Modules which are known to be fitted with the incorrect MCU:
URUAV TMX5 Lite
Vantac MPM Lite
Modules with the incorrect MCU have been unreliable and have experienced erratic and unpredictable behavior.
The correct MCU part is an STM32F103CBT6. This version of the STM32F103 has 128KB of flash memory. The incorrect part which is fitted to the modules mentioned above is an STM32F103C8T6. The C8 part officially has only 64KB of flash memory.
It is known that many STM32F103C8T6 chips actually do have 128KB of flash, but it is not guaranteed and cannot be relied upon.
The easiest option is to replace the module with one which has the correct MCU. You should also complain to the manufacturer or vendor of your original module and ask for a refund.
For most people, this is the recommended option.
If you have the tools and skills you can replace the MCU on your module. You will need to de-solder the existing MCU and replace it with a genuine STM32F103CBT6. Although it is not easy, several people have done it successfully.
This option is only recommended if you have the right tools and soldering skills.
You can download the MULTI-Module firmware source from Github, disable the flash size check, compile your own firmware build, and flash it to your module.
Instructions for downloading and compiling the firmware are available on the Github repository.