-connection timeout (check the settings in the web interface)
-hardware issues with the adapter itself
-general slow transfer due to used serial protocol
I've done some research and it looks like the adapters require stable input voltage of 5V, via USB for instance:
Module parameters:
1) The module adopts ESP-12S, which is based on ESP8266's low-power UART-WIFI chip module;
2) The main frequency supports 80MHz and 160MHz;
3) Spectrum range: 2412-2484MHZ;
4) Logic voltage: DC 3.3v;
5) USB input voltage: DC 5V;
6) Size: SD-24mm *58.3mm; TF - 24 mm * 45.5 mm;
7) Transmission file name format requirements: only support the file name consisting of ASCII code;
8) TF card memory: 128M.
https://aliexpress.ru/item/400099142585 ... web201603_