I have compared my scanners side by side and I get almost identical performance on WISCOM regardless of make and model. When I do miss transmissions, many times it is off just the Chilton site and in the past it drove me nuts. But what I found was the unit that was transmitting was in a bad location and my scanner would "blink" back and forth from scan to receiving a transmission, and finally I caught the dispatcher saying one day she wasn't able to copy the unit. So the site itself must have been keying and unkeying quickly as it caught some good packets and then lost some packets.
I usually have my Whistler WS1040 on WISCOM and it does great, but it doesn't decode the unit IDs correctly. It will always show an ID of zero. My SDS100 and 200 decode them perfectly, so it is nicer with them, but I only listen to WSP and statewide interop stuff, so I don't really care about the IDs. Plus, just like you I don't have any simulcast sites near me so the SDSs are overkill. I use them for Outagamie & Winnebago's simulcast system instead.
I would suspect intermittent interference of some sort near you with the control channel on whatever site you're monitoring. Have you tried using attenuation or IFX on the control channel? My advice is to investigate it further as the SDS200 is overkill if you don't monitor a simulcast site. The 536 is a great scanner and should receive WISCOM just fine unless there are mitigating circumstances.