What could prevent a firmware upgrade?

[wsw70]

One of my Sonoff Basic was behaving erratically (sometimes available, sometimes not) and I decided to reflash it with the latest dev firmware.

I can reach it via the web interface, the API and telnet. I tried to reflash it with the dev (bit also master, and even (sorry - that was just for tests :)) Tasmota) via

• the web interface: I chose the firmware, pressed Upgrade, the blue rectangle below the form appeared (but did not show any progress) and nothing.
• the API: the connection was successful (100 Continue) but ultimately failed
• telnet:

[661157] [TELNET] Client #0 connected
ota http://192.168.10.251:8000/firmware.bin
[667996] +OK
[674935]
[674938] [EEPROM] Reenabling EEPROM rotation
[674939] [OTA] Disconnected

Basically nothing happened, I am still at 1.13.5.

I also tried to factory reset before retrying all the flashes above.

What could be the reason for the firmware not accepting to be reflashed?

I will ultimately reflash it via a cable but wanted to understand what could go wrong. Beside the refusal to reflash, the other functionality is OK (switch, MQTT, ...)

[mcspr]

#1631 ?
set loopDelay 10 and reset should do it

[wsw70]

That was it, thank you!