A cold start trap for many devices with the same exact time stamp most likely indicates a singular trap was asserted across multiple device models.
Check the USMOtherIPAddesses (0x5b60004) attribute on some of the devices for the same IP address.
When a trap comes into the Spectrum server it will assert the Alarm on all devices where the source IP exists.
Release : 10.3.2+
Component : Spectrum Core / SpectroSERVER
Set UseRPAForTrapProcessing=TRUE for the devices in question.
This can be done in bulk against multiple device models via the Spectrum attribute editor
Enabling the above will exclude the overlapping IP Addresses from being used during trap processing.
Please refer to ArticleId 140583 which is linked under the additional information section for more information.