Hard to say, other than if you are having difficulty tonguing freely / naturally in all registers (generally) then you must be doing something that is unnatural–that is to say against the most efficient way of playing.
I recall early on having difficulty tonguing a bit myself. I don’t recall having a tongue-in-cheek feeling, but I recall feeling that I was better at slurring than tonguing–that my newfound range was not useful in that I couldn’t articulate.
So I started doing some scale exercises that went through all registers I could play and worked on playing some music that involved articulation.
Before too long, it wasn’t a problem anymore.
I have found that less seems to be more–that when I overthink things or try to take a linear-straight line approach to playing, I overdo something and get in my own way.
When I stay relaxed, only do the minimal amount needed (air, tightening the corners), my sound, resonance, flexibility and range are best.
I have limited time to practice as well–I am an amateur with a day job and family responsibilities, so I try not to spend 100% of my time doing harmonic slurs throughout my range and trying to push the envelope the whole time (“gladiator trumpet”)–I have caught myself doing that and that has led me to bad habits, which seem to come quickly and be hard to get rid of.
I think I’m getting better and identifying when I am tensing / pinching my lips.
I also think I was playing with too forward or puckered of an embouchre early on–I could only play deeper mouthpieces, when I tried playing a shallow mouthpiece I bottomed out. I’ve been playing a shallow mouthpiece for the past couple months and it feels natural now and good and I think it’s helping me play with a flatter (I think) and more efficient (I think) embouchre.
Perhaps you are overthinking / overdoing the pucker thing a bit, perhaps like I was. The aaah ooohh is critical in mindset in ensuring that I tighten the corners (only as little as necessary and slightly/gradually) rather than clamping down top to bottom in the middle and cutting off the vibrating surface, rather than letting the top middle lip vibrate freely in the air column. But it’s more of a feeling of being relaxed than being puckered and forward the whole time–Greg doesn’t play with a pucker / forward embouchre 100% of the time in all registers.
Good luck–hope you work yourself through this temporary setback. I know how frustrating those can be. Perhaps play some music and focus on the sound and experiment with what gives you the most resonant, open sound and allows you to articulate freely–that may help give you a clue into what’s going on.