I noticed strange thing. Lexemes from L20540 to L20543 just disappeared. They were neither merged, nor deleted. They for sure existed because they were created by me and I document every Polish lexeme I created on [[ https://www.wikidata.org/wiki/User:KaMan/brudnopis | this page]]. As far as I remember they were created 13 September (after datacenter switch) and they disappeared 10/11 October (after datacenter switch back). Could it be that this is related to https://wikitech.wikimedia.org/wiki/Switch_Datacenter#Schedule_for_2018_switch ?
Action plan: T206743#4658146
Missing rows timeline: T206743#4658274
Cloning hosts progress: T206743#4658362
The only section affected was s8 - T206743#4665589