Well... this is utterly bizarre, but the errors have disappeared; I have no clue why this would be, I just went away for a bit and did something else completely unrelated and they're gone and it's all behaving correctly.
The only thing I can think of is that I had a browser window open with an expired session that I closed in-between looking at Telescope.
If anyone can confirm this would cause this behaviour it would be appreciated, otherwise, I will just put this down to strange weirdness, forget it and move on.
I have so much to learn...