talliar, you say that on April 1 your coins are still in the wallet - so something is happened in the next 2 days with your phone. Try to remember if you downloaded an app during that period, did you notice anything strange on your phone?
For how long you keep your coins in that wallet, do you have 1+BTC for a long time, or you just transfer that amount on April 1?
If
this is the outgoing transaction he is talking about, he received the coins on April 1st into 2 different addresses. Both of them had had a lot of movement in the previous days, so if I had to take a guess, they came from a mixer/exchange/similar.
It may be a long shot, but I've read about user installing the "Houseparty" app had had many data leaks and some even lost BTC. Since we are in lockdown, it's likely he installed it, and it would be inside the "pretty famous" list of apps.
No, I never heard of this application and did not install it on the phone. I am from Russia, sometimes new trends go up to us sometimes)