This is enough to show that the title of your post is erroneous, and you have probably learned all you need to learn about HC-05. I would be very suss about reply #2. While it seems not to be really necessary, it IS good practice to to ensure 3.3v at Bluetooth Rx, but the way you are doing it is the way everybody else does it, and surely not the cause of your problem.
For all that, I can't say much about what the problem really is, but I suspect it is all about timing, even though I note that you do have a delay in the loop - a large one, not a small.
Since you are smart enough to use hardware serial, two options offer themselves:
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Even though I understand the serial monitor is working perfectly, you might just try having it run simultaneously with Bluetooth, Thereby checking that the problem really is exclusivel to Bluetooth.
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You might configure Bluetooth and monitor to run at 115200, as this might be one of those times when speed really counts.
This might be the time when you need to know something about data buffering - something I know nothing about. I also know nothing about reading pots, but I assume that the code is essentially kosher - just needs a bit of tweaking
You appear to be using Morisch's terminal, which is essentially the go-to app these days, and I don't think there is anything to be suss about there.