According to Official Guinness Records,
The most people on trampolines is 375, and was achieved by Geylang Serai Community Sports Club (Singapore) at The Lawn @ Marina Bay, Singapore, on 8 July 2017.There were 376 trampolines and 376 participants. One participant was disqualified as she took a break to take a selfie!
For a complete list of 2017 records, please visit 2017 Guinness Records in Singapore.