OK cool, I'll try that, thanks!

A couple of questions about it....

Which resistors specifically?

Voltage dividers exist on the I2S pins. The I2S pins are working perfectly and I would be concerned about changing them. Not just because of "if it ain't broke don't fix it" but also because the whole reason they exist is to protect the WT32i chip from being fried. Though, if you say that those I2S lines might possibly be related to the serial port issue, I'm willing to try.

There is the voltage divider on the reset line. It is inactive (in "read" mode) when I am reproducing the issue. If it's not doing anything when the bug is happening, my guess is that it can't be related. Though I'm not sure because EE surprises me frequently and you know much more about that than I do.

The only remaining voltage divider is on the Arduino's TX2 line that runs into the WT32i's serial RX pin. That's not where I'm seeing the issue recur, rather, I'm seeing it on the WT32i's TX line (the one coming into the Arduino RX2).

I actually don't know if the WT32i's RX line is encountering the corruption or not, because it's necessary to have local echo turned off on the WT32i for smooth software operation. Though I suppose I could certainly turn it on briefly to test it and look for a problem. Though interestingly, even if I did that, I wouldn't be able to tell. I would be getting the data back through loopback echo from the WT32i, coming back on the same channel that's encountering the bug. So I wouldn't be able to tell if the issue was in the transmit or the receive in that case.

I do not have any resistors at all on the WT32i's serial TX line that runs into the Arduino's serial RX2 pin. And yet that is the place where I see the text being occasionally corrupted: Messages from the Bluetooth are sometimes turning into garbage characters on their way into the Arduino. (This is not a buffer overflow by the way; buffer overflows drop characters, and this is not drops, this is corruption.)

Do you think that possibly it might be caused by not enough voltage on that TX line coming in from the WT32i?

I think I have a bag of 1k resistors around here, and I definitely have a big bag of 10k's but probably not any 5k's (though I'll look again). If I wanted to test this in a hurry with what I have on hand, which do you think would be better, swapping out the 10k's for 1k's, or, doubling up the 10k's in parallel to make 5k each?