You do have to engineer things properly.
Hardware needs good stable 3.3V power able to sustain peaks of 400mA with a good decoupling capacitor close to board.
The firmware should also be written to ensure there is no sustained delays which may trigger the watchdog timer and to handle and recover from any failures in accessing AP wifi network.
I think many of the previous reports of instability were down to power supplies and software structure.
https://github.com/martin-ger/esp_wifi_repeater
I only have 1 of 3 Wemos d1 boards running this. i have grounded gpio0 to ground as suggested. Any idea what i'm doing wrong?