Upvote:2
I got to travel with this situation and I was let through. The lost and found passport is considered as expired in this case and you can travel if you did not report the visa being lost.
Upvote:3
When you find the old passport, you should quickly bring it to the issuer authority (or police).
Lost passport are usually considered stolen, so they are stored in invalid passport databases. By having it (or worst, by using it) you get a lot of trouble.
You should care much more about passport (not lose it). It is a security and safety hazard. (because of possible use for criminal activities, which include impersonating you for bank credit).