How to find lost records?

Question

Python

I have to match records by 2 characteristics. The first is the date of the event and the second is the start date. I take from the database like this

heh = list(db.events.aggregate(
[
  {"$match": {"eventName" : "Purchase Hard"}},
  {"$group": {"_id": "$uid", "dateofpay": {"$addToSet": "$updated_at"}}},
]))

lel = list(db.events.aggregate(
[
  {"$match": {"eventName" : "Level 1"}},
  {"$group": {"_id": "$uid", "dateofstart": {"$addToSet": "$updated_at"}}}
]))

in theory, the first query gives about 1600 records, after this comparison, they remain about 850:

dateoflvl1pay = list()
for players in lel:
  kost = players["_id"]
  if kost in x:
     dateoflvl1pay.append(players)

moreover, such a query produces the same 1600 records, that is, all 1600 must have both "Level 1" and "Purchase Hard"

= list(db.events.distinct("uid", {"eventName": "Level 1"}) and db.events.distinct("uid", {"eventName": "Purchase Hard"}))

please tell me how to solve this problem.