I too have been having this problem with an iPhone 4S after update to 8.3. However after taking note of all above, I have found that the problem seems to reappear approx 7 days after its has been cleared by whatever action you take. So it keeps coming back once you can stop it in the first place.
The errors og getbufzone incorrect =0 causes FSTaskSchedule to panic crash. Under the Diagnostics and Usage Data, there appears two logs created each time it crashes. One is the bug 110 getbufzone in FSTaskScheduler and the other is RESET COUNTERS which is bug 115 (which I think may occur just ahead of the getbufzone error. This all happens when the iPhone does a reset taking between 4 and 8 minutes to repeat the error. At this stage the only way I can get it to charge is to plug it in and then shut it down. It still charges.
I have also noted that any activity on the phone whilst plugged in cause the delay to any crashes. ie. if I use the phone its OK, but leave it idle for 5 minutes or so and it starts its crash sequences.
Looking at the syslog just prior to crash shows the start up of FSTaskScheduler and then 10-15 seconds it crashes.
Jun 3 09:25:24 iPhone wifid[70] <Error>: WiFi:[454987524.458931]: Disable WoW requested by "apsd"
Jun 3 09:25:33 iPhone com.apple.xpc.launchd[1] (com.apple.OTAPKIAssetTool[163]) <Warning>: Could not find program specified by service: 2: No such file or directory: /usr/libexec/OTAPKIAssetTool
Jun 3 09:25:33 iPhone com.apple.xpc.launchd[1] (com.apple.OTAPKIAssetTool[163]) <Notice>: Service setup event to handle failure and will not launch until it fires.
Jun 3 09:25:33 iPhone FSTaskScheduler[164] <Notice>: Started
Jun 3 09:25:33 iPhone findmydeviced[162] <Warning>: findmydeviced has been launched
Jun 3 09:25:34 iPhone findmydeviced[162] <Notice>: (Note ) MC: User has completed cloud configuration. Not showing UI again.
Jun 3 09:25:37 iPhone locationd[64] <Warning>: PLClientLogging: log locationd withContent {
} cannot continue due to nils!
Jun 3 09:25:47 iPhone syncdefaultsd[97] <Notice>: (Note ) marked "com.me.keyvalueservice" topic as "enabled" on <APSConnection: 0x17569c70>
Jun 3 09:25:49 iPhone mobileassetd[108] <Error>: mobileassetd - updateAssetMetadata: unable to perform asset metadata update: Error Domain=MobileAssetError Code=30 "The operation couldn’t be completed. (MobileAssetError error 30.)" UserInfo=0x17dd2f90 {NSUnderlyingError=0x17d82670 "The request timed out."}
NOTE - after you "fix" this problem this task is not activated as shown above .... But it starts to reappear again after 7 days.
I don't know if its related but this seems to have become a problem since I have been "offline" from wifi for most of that time as I have been on the road for most of this time of this problem happening. Back home it always found my WIFI on when the phone was likely to have been plugged in...
OK - so here is how I seems to get 7 days worth on "fix". Close all apps on the IPHONE then I use ITUNES on a windows PC, connect iphone (and quickly before it has time to reset), Tell it to do a RESTORE, let it do a backup, ignore that its going to clear the phone, Accept it wants to reload 8.3 but because I don't have the IOS image currently downloaded to the PC, I abort the process (as it tries to download IOS 8.3), manually restart the phone and the problems appear to have gone and I don't seem to loose any settings or apps etc.
I have been trying this now for the last 2 weeks and each time something along this steps has been working. I have also been using IBACKUPBOT to view the system log file and validate the backup but at this stage I am not sure its doing anything else.
I had tried the RESET ALL but this didn't appear to work for me. I wasn't game to do the ERASE ALL albeit that the same message that happens when you do the RESTORE so I don't know if this would work.
I previously tried removing apps, resets, etc etc but nothing worked but he above.
I believe this is an apple IOS problem but since I cane find out what the heck is FSTaskScheduler and what it does I cant be sure why this has started happening.
Cheers to all and I will update once I find anything more at the next 7 day period!!