Same here. They have a known bugs where entries will vanish from your contacts. Data loss is a big deal (or so I thought).

Support asked me to let them know when a contact vanishing did so they could gather logs from me phone.

Once I was finally able to see it happen, I reached out. Reported that it had just happened overnight. The customer support said it was too long of a time frame for engineers to investigate because "it generates a lot of logs and that's too much to go through". I could not believe their answer.

I just moved my contacts to Gmail and that was the end of it.