Thanks a lot

I own a laptop
IdeaPad L3 15IML05
A year ago, I bought a ddr4 - 2666 16gb
According to the information on the site here, the memory is compatible with the product:


The memory has been working normally, for a whole year, but two weeks ago it no longer supports the system.
The installed memory has become only 4 GB RAM
The system now works on 4 GB instead of 20 GB !
I checked the motherboard and all the ports, and made sure there was no problem.

Please help and thanks.