hmmm... We've seen issues with PE4 but I'm not familiar with this. I'd keep an eye on it to see if it's repeated. Pay attention to what architecture it is if it happens again, though I don't think that's it.
Forced mode vs IPHelpers shouldn't have anything to do with it because both of those options are off-box and shouldn't impact the PXE server at all. Doesn't mean it's impossible, but if IPhelpers are a problem, we're in trouble. With the advent of a mixed environment of UEFI and BIOS systems, IPhelpers are required because DHCP forced mode can only handle one or the other environment, not both. If therefore IPHelpers are causing problems, we're in severe trouble.
That said, possibly scale? How many PXE servers?? Or is this just on a single DS, since I noted you simply renamed the folder and didn't indicate you had to visit several boxes...?