I have the following problems after upgrading to 2.8;

1) I cannot add or remove tags from items in the front end
2) When I save an item in the front end, it just remains on the same add or edit screen

So, I wonder can I just revert to the previous 2.7.x version? is that possible after installing 2.8?
And if not, can you tell me how to troubleshoot these issues or is there a quick fix that I can make to fix the problems?

Many thanks in advance. K2 is a key component on my website and I love it (also SIG PRO) but this is causing big problems for me!

Hello,

This is either a jQuery conflict (multiple or no instances) which jQuery Easy can resolve

or an outdated override. I would start by removing the itemform.php overrides from your template.

Thanks for your help but I have decided to abandon the 2.8 installation and do an emergency restore from backup of my whole website. An expensive lesson. $150 including developer time. There are simply too many critical issues with 2.8 to try to get them fixed and make the website useable again. It would be good to know if I could have simply re-installed 2.7 to save myself a lot of money :)

150$ for a restoration is a bit steep.
Use Akeeba Backup for free or you can choose a hosting plan (on the future) where you can backup ad-hoc your entire site.

As for reverting, if there wasn't a catastrophic issue it might do the trick
getk2.org/downloads/?f=K2_v2.7.1.zip
getk2.org/downloads/?f=K2_v2.7.0.zip