A fellow 8 month old owner here - also experiencing quite a bit of regression on things we thought we'd tackled, especially with jumping up at counters, picking up all of the things and the famous spaniel rubber ears! From everything I've read or been told, it's all about staying consistent and as Penny says going back to basics. I'm trying to keep my cool and use the same training methods I used when she was a baby and not introducing anything new as that can confuse their already confused little teenage brains.
It's been hard work so far, but still preferring this to the little cockerdile wee machine stage to be honest! I think it's because I can still remember my turbulent teenage years (only just) and how out of sorts I felt sometimes.
We'll get there with our pups - we've made it this far! (I was going to say 'and we'll look back on this time and laugh' but not sure I'll ever find my girls personal mission to try and eat every toxic plant on the planet funny!!)