Bass leaves after amp warms up?

"What is the solution?"

Hasn't changed.

Need to change amp or speakers, until you find the combo that floats your boat. It's called a system upgrade, right? Assuming speakers stay for now and amp changes, switching to a more beefy dedicated power amp that can double down to 4 ohms would be the most effective strategy to follow to help cut to the chase.

Fish, until you make a change to try a more effective pairing of speaker and amp, not sure there is much else to say.

Once you have that in place, then additional tweaking may or may not be needed as well from there. IT all depends on how "finicky" you are able getting a particular sound that you seek. Its the typical scenario for any "audiophile" . It may take some time and money but if enjoying your music to the max is your goal, it should be worth it in the end.

I expect to try Musical Fidelity M6 amp 250w next week
I also have someone coming over with SPL meter
In addition,CablePro Revelation power strip to try.
Otherwise I'm exhausted
Thanks to everyone
I will report back

One thing to add is that a less than optimal speaker/amp pairing does not necessarily mean that either device is faulty or defective. Just that they are not the best match for each other electronically.

Given that, depending on how long you have owned the amp or speakers, the best one might expect from a dealer is perhaps some trade-in value towards an upgrade. That's fine. Live and learn! If it has not been too long, a good dealer might offer full trade value, but even that is not a guarantee.

So if you want to move forward, find out what your dealer can and will do for you, but consider other buying options as well, including buying used to help minimize the loss when you try something that may or may not work out, which is often the case when one has discriminating ears.

I can't assume a dedicated power amp will solve the problem till I try.