Ok, on 15.5, using BIOS setting "Sleep State: Linux S3 hibernation" behavior is different than I observed on 15.4. I'll mention than on 15.4 I use full disk encryption with discrete partitions, while 15.5 is just one ext4 root partition and another swap partition, non encrypted. Hibernation appears to succeed, but on restore I don't see it attempts to read the sap image, it boots fresh. I will attach both journals, from hibernation attempt, and fresh boot.