I can feel you and your frustration with UART-reading.
I’ve done a lot of UART OBIS-stuff in the last months, so I suggest you debug first if the crashing/ unreponsiveness is related to memory being exhausted.
I’ve got fully working code for reading obis codes from uart with debug only for diffrent board, maybe you can learn from it also for your use case?
And maybe as you’re reading obis codes from UART, you might even use my modified esphome-component? Check it out too as it is much faster and more efficient than debugging UART, maybe it will work for you.