Hi there, I'm assuming that you've selected Serial transport for remote control. Up until now, I don't think anyone has used Serial on these devices, most menu's up till now have used WiFi.
This seems to be because the ESP8266 Stream.h class is lagging significantly behind the true Arduino implementation.
I'll raise a bug report for the designer UI to conditionally change this to use "available" for ESP8266 boards (and I'll check ESP32 while I'm at it). There's a patch release to upgrade IoAbstraction with new features due soon, I'll add this to that release.
This is unfortunate because the semantics of the two methods are very different and it means on lower speed serial connections with a lot of updates (100-1000 per second range), you could risk locking up the board when serial blocks because it can't write. Although this is unlikely in most applications to be fair. I've tested the protocol down to 9600 baud, and it doesn't even saturate in most normal cases.
One possible tempory workaround (that needs to be repeated after designer code generation):
Open SerialTransport.h
change line:
virtual bool available() { return serialPort->availableForWrite();}
To:
virtual bool available() { return serialPort->available();}