Server suddenly developed lag spikes when playing anything higher than 4Mbps quality

Server suddenly developed lag spikes when playing anything higher than 4Mbps quality

For Server suddenly developed lag spikes when playing anything higher than 4Mbps quality and the Plex I'm not sure what's going on. I am sure this is a server/network issue but I can't lay my finger on the source. I used to be able to any movie at max/original quality (most are 12Mbps) without a hiccup. Now it seems like I cannot play most items above 4Mbps without serious lag spikes. I'm not sure when it started since I haven't been home to actually use full bandwidth much but my fiance tells me it started about a month ago. It also doesn't seem to matter what I'm playing the videos on - cell phone, tablet, web, Chromecast V1, Chromecast V2 - they all develop the spikes.
My server Specs:
Plex Server:
Xeon E5-2675 CPU
2x Gigabit LAN connecitons set up as a team.
The big issue is the lagging when to the chromecasts because that's what we use most. The old version 1 chromecast is the only device connected to that particular wireless network and is about 5 feet from the wireless access point. In the past, with the limits of the 2.4Ghz band, this one couldn't always do 12Mbps+ but was happy at 8-10, now it's down to 4 tops. The version 2 chromecast is connected to a different access point on a 5Ghz wireless AC band. This one is about 10 feet from the access point with nothing but the TV between the chromecast and the access point. Both access points are hard-wired to the same central switch as my server, all devices supporting gigabit speeds (tested and confirmed).
I have tried rebooting my PC, the switch, main router and all the access points to see if something was just needing a refresh and that didn't work. I've also tried playing with the transcoder settings, trying Automatic, High Quality, High Speed and Make My CPU Hurt and they all lag.
I'm attaching a log file I got yesterday. I started a new movie (the second Austin Powers) around 3:22pm and it was immediately laggy. Looking through the trace myself, I did see one notice of excessive buffering detected in middle of it spiking but it couldn't nail down the source. I also see this a lot:
WARN - Held transaction for too long (..\Sync\SyncItemGenerator.cpp:105): 0.140625 seconds
Not sure what that means but there were not devices receiving sync updates at that time. Log is showing the V2 Chromecast. At the time of running this, the only items active on my network were my server, this chrome cast, my cell phone which was controlling the cast and a desktop PC that I was at getting the log files from. CPU usage on my server maxed out at 15%, with only 8% of my RAM used.
Anyone have any ideas on what's causing my lag spikes? As I said, it used to work great at higher qualities and hardware and software wise the only changes have been plex updates - I haven't touched anything else. All my hardware passes diagnostic tests which while not perfect give me some confidence that it's not a failing hard drive or bad stick of RAM.