Google Pixel 2 - bluetooth volume not increasing/decreasing properly

I have a Google Pixel 2, works great but every now and then on my bluetooth headphones, the volume doesn't work properly.

It's hard to explain, but basically it's like it's only the very highest volume, and the lowest couple of levels actually change the volume - everything in between stays exactly the same.

So if you imagine ten 'levels', then if you set it to ten, the volume is very high. If you set it to level one or two, it's very low, if you set it to anything in between it doesn't make any difference and it's either very low, as if stuck on level two, or very high, as if stuck on level ten.

It only seems to happen with my earphones (not bluetooth speakers as far as I've noticed) and rebooting the phone has worked in the past in resetting it.

Has this happened to anyone before? Is it an Android/Bluetooth quirk or something with the earphones? The earphones are TaoTronics TT-BH07 - relatively affordable on Amazon but with a massively favourable rating - like 4.5/5 with over 10,000 reviews, they feel really good quality.

Thanks in advance,

No ideas on this one?

The Bluetooth volume seems to work properly for me on the following: car (2015 Kia Forte), over-the-ear headphones (Sony WH-H900N), external speakers (UE mini Boom, UE Boom, Bose Soundlink Mini). I don't really pay much attention to the volume graduations, so I can't say that it's a 1:1 correlation between the volume rocker, the volume slider position and the actual volume.
And of course, in the car I'm using hands-free on the steering wheel to adjust the volume through the car speakers, so the actual media volume on the phone never changes once I've set it at maximum.