I have lost my buy boxes

I have sold books on Amazon for 14 years.

Last month, I used to have from 1 to 4% listings with buy box and sales were very good, so much that I was planning to enlarge the business.

Then, suddenly, I have lost them all.

I have checked my performance, it's healthy, 0.92 errors (one negative feedback last month, 96% year feedback, 97% lifetime, everything else is perfect).

Selling books on Amazon is like crossing the Ocean on an Inflatable boat: it's easy to capsize.

I have checked my listings, in 40% of the time, the buy box went to Amazon, 10% to other sellers, 50% to nobody.

I have enquired with SS and they sent me the usual boiler plate reply.

Either the algorithm is on vacation, or it has decided to eliminate small booksellers.

Any suggestion?

Guy