I think the op is just talking about people not being collected in quick time.
Locallity of services and traffic will be cause, or level of service.
The other thing it could be is a death wave, these are still in game and have not been patched out, it is part of game
OP please clearify, but this below might help
Deathwaves are cause by a combination of factors,
Massive in flux of pop, not just zoning on pause. The end of last wave, after accident what ever, zoning lots of high res
Stingey Mayor, skimping on death care. Not dissing on people that have, its a great way to make millions if your like me and dont cheat
Traffic gridlock and locallity of sevices
Zoning industry could cause it due to a demand spike in res
Park building spree leveling up buildings, particularly high res
Skimping on heath doesnt help either, cause dead people lower heath, giving more death at mid point of wave see above about making millions
Industry clogging roads is probably root cause of traffic issues, rail network your freight
Cems have more herses than crems, a consideration
If cems are full and you have enough crems, you can click empty on all to transfer bodys to crems, this keeps the locallity of cems working
But trust me OP, as a fellow vanila player.
pop influx, traffic and skimp together = death wave