Can speakers sound worse during break-in period?

I purchased a NOS pr of speakers ( I’m not disclosing their name. Not interested in hearing from their haters) and was really liking them before I started to seriously break them in. It seems like after 24 hours they seem to have changed and sound worse, or not as good as they did. Are they just going through changes with some drivers opening up faster than the others? I know there are many components involved in this process and some might be a head of the others. I’m assuming that’s the case and when everything comes together they will sing.
Do I need to 'burn-in' my Harbeths?No: the only component part of a Harbeth loudspeaker that can change as a result of 'burning-in', is the resin-doped cloth suspension that centres the neck of the cone in the magnetic field - sometimes called the 'spider'. Under the microscope, once the resin-cloth has been worked backwards and forwards, it crazes into millions of small interconnected islands. This process is irreversible and takes only a few hours with bass heavy music played a little louder than normal. After that point, the drive unit can be considered fully stabilised with the resonant frequency settled to its final value. The ferrofluid used in Harbeth tweeters becomes appropriately viscous after a few minutes operation. Neither the coils, resistors, capacitors, cables nor any other part of a Harbeth speaker has any short-term ageing mechanism.
so i was right. burn in is a hoax
But burn out is not a hoax. 🤗
If you check with the manufacturer, you will get the answer to your question.  Typically, Magnepan tells customers that there will be a period of adjustment as the mylar does experience come changes from new.

Why is this an issue I can't understand as every manufactured physical and electronic item in the world changes with use and time.  I know the wonderful 327 in my C2, which is 53 years old, is not performing identically to its first day on the road.  For this, I am thankful, by the way.

Your manufacturer will be pleased to discuss this with you, I am sure.

I noticed that sound changed over initial period with speakers and earphones. Not with other things. Real or my imagination is another issue but it happened every time that I can remember.