1) How do I prevent Bittrex from selling my altcoins automatically? I don't see the "auto-sell" option any more.
click on Lab ---> Auto Sell.
Check whether you have enabled the automatic sale of any of your altcoins.
2) How do I buy altcoins again on Bittrex in the new interface? I don't see a way.
I love the old interface but there are few problems regarding the new:
The tokens/dollar value does not appear.
It seems that all your problems are in dealing with the new interface, this video from YouTube will help you interact with the site again
https://www.youtube.com/watch?v=-y8rYJns9sgOh that is a good video, thank you for sharing it. I was wondering why they no longer showed the dollar value for some of my tokens. I do have one issue I cannot fix, though,,, how do I force a coin to show up on my wallets list first? For example, I have to scroll to 3rd page every time I want to see my balance, can I bring it up to page 1, does anyone know? Old Bittrex had my coins listed if I hid the others, but I could not hide coins on my new screen now.
This is the thing i dont like on the new UI where there are really some features doesnt suit out my needs unlike on bittrex interface before where you can able to hide those coins if you wanted but now you would really need to scroll into other page just to check out your balance which is quite awkward.
Going back into the topic. It is clearly the auto-sell feature is still on thats why it do autosell, for it to be stopped then instructions above had already given and you should follow those steps.