Hi guys. As fact additional heatsink didn't help too. For few days it worked fine but then again got freezes every 4-8 hours. So this is was definitely not a overheating problem. Sorry that I did not check everything completely and mislead everyone. Also was wrong about back heatsink. I'd disassembled it and noticed that heatsink for CPU only. So, CPU has two heatsinks on the top and on back side. Memory and eMMC has no heatsinks at all. Yesterday I had reinstalled FBSD completely from scratch with UFS on internal drive again. I don't hang up And will look how it gonna works. Probably reason of freezes was in ZFS. I hope so. See you later.