In this case, clearly the problem is extremely slow work of SSD, due to lack of space.
How to build-
- Keep at least 30% of the disk free, and make sure that TRIM is working.
- Better yet, set aside 20-30GB under over provisioning (ie leave Unallocated, after performing a full wipe of the disk), then it doesn't matter how much free space and does TRIM.
Ie SSD you have is serviceable and works normally. It is extremely slow in some situations due to the tough operating conditions.