B737 Captain reported the number 1 engine-driven generator and the Bus Tie system malfunctioned during cruise flight. Due to weather and the potential safety hazard of the malfunctioning systems; the flight crew opted to divert to an alternate airport.

Narrative

We lost #1 engine-driven generator during cruise at FL370. Followed the QRH and generator was reconnected. A couple of minutes later; the #1 generator failed again but the Bus Tie did not automatically pick up Transfer Bus 1; which resulted in numerous failures. The Transfer Bus Off light did not illuminate; which was confusing. We started the APU and when selected; the APU generator did not pickup generator #1. After a couple of minutes; we tried again and the APU generator successfully picked up generator #1. We decided to divert while enroute to ZZZ to ZZZ1 due to the seriousness of the Bus Tie relay not working correctly; ZZZ was holding for thunderstorms; ZZZ1 was clear plus has Company maintenance. The landing in ZZZ1 was uneventful. By the way; we accomplished an engine run for maintenance in ZZZ3 before departing because Maintenance worked on the #1 generator and wanted to make sure it worked since it had failed on the previous flight. The plane; Aircraft X; recently came out of a heavy C check. We couldn't find in the QRH or AOM the specific components that would fail if the Bus Tie system does not work.