The sit is slower. The recall is optional. The loose leash lasts until the first lamp post. Six weeks ago all 3 of those worked, and you have started wondering whether you imagined it.
You did not, and none of the training has been deleted.
What the research actually says
Dogs show reduced responsiveness to the cues of the person who raised them around the onset of adolescence. That responsiveness returns later in the stage. This is development rather than a hole in your training.
The useful phrase is apparent regression. The behaviour is unavailable right now, in the places where it is hardest. It is usually still available in your kitchen.
Prove that to yourself in 4 minutes
Stand in your kitchen with 10 treats. Ask for the 3 things you taught first, once each, in a normal voice.
Count how many you get. Most owners get all 3, which tells you the behaviour exists and the context is the problem.
Now ask for the same 3 things in your front garden. The gap between those two lists is your actual training plan.
What to do for the next 8 weeks
Drop the difficulty everywhere by one step. If the recall used to work at 30 feet, practise at 10 feet. You are not going backwards, you are training where your dog can answer.
Pay much better than you did at 5 months old. Adolescence is the most expensive stage to train, and the competition outdoors is at its strongest.
Manage whatever you are not currently training. A long line, a closed door, a leash on indoors when guests arrive. Behaviour change is built from management plus reinforcement, so management is half the work rather than cheating.
Pick one skill at a time. Owners who take on recall, leash, jumping and settling in the same week get 4 half-trained skills and no confidence.
The one thing that makes this worse
Repeating a cue that is not being answered. Every unanswered sit teaches your dog that the word sometimes means nothing. Say it once, wait 3 seconds, and if nothing happens make the situation easier rather than saying it louder.
Reward-based training has been associated with higher reported responsiveness and fewer reported problem behaviours. Aversive methods, sold as the fast route through this stage, are associated with worse welfare outcomes and no training advantage.
Safety note
Apparent regression happens over weeks. A change that happened over days is different, and so is any new growling, snapping, freezing or hiding. Book a veterinary examination first, because sudden behaviour change warrants one and pain often presents as a change in behaviour.
How long it lasts
The stage runs roughly 6 to 24 months, and the worst of the ignoring tends to sit in the middle of it. Responsiveness comes back onto whatever you practised while it was gone, which is the argument for doing something small every day.
Tonight's version, in one line: 3 cues in the kitchen, the same 3 in the garden, and train the gap.