Lync 2013 client not processing history spooler folder (conversation history)

Question

We have been using Lync 2013 fully patched up to latest & greatest, along with Exchange 2013 for about 6 months now & everything is working
great. (I did a AD migration from our old parent company in the UK as well as migrated exchange from 2010 to 2013, all that without a hitch for the most part.)
the issue that seems to be popping up intermittently is conversation history. I manged to work around some of them for the most part & getting
them to process; with the exception of 1 user.
If he logs into another PC his conversation history works fine.
However on his PC it does not seem to want to process the history spooler folder in "C:\Users\User\AppData\Local\Micros­oft\Office\15.0\Lync\[email protected]­m",
there are 737 files in there (all of his convo history)
Now what i did & it seems to sort of work is,Signed out of Lync, I deleted the users Sip folder after backing up the history spooler folder, logged
back into Lync which recreated the sip_user folder; logged back out of Lync , copied the History Spooler folder back to the SIP folder, & signed into Lync.
This took 10 files out of the history spooler folder, & then appeared in the convo history; both on Lync client & Outlook; but did not bring
all of them in. I did some testing and if you log out, then back in, it processes a few more. but not all.
EWS & MAPI settings & all other Lync configuration information settings match a users with no convo history issues.
So now the questions. 
1)What could possibly cause what ever mechanism that processes the History spooler folder to stop/only process a few items during sign in? Also what
is the mechanism? 
2)Is there any way through powershell to force the synchronization of the history spooler folder?
Thank you

Answer 1

so in some more testing i had check the history spooler folder, & there were about 700+ files.
as a note* (Upon deleting the users sip folder & logging back in thus re-creating the folder new convo's where saving. So i did "fix" the issue with no new convo's during my initial work prior to opening this thread.)
I then removed a good chunk of the *.hist files & only left convo's from this month. signed out then back in, 10 files processed. then did it again, another 10. did it again, & it did 4 then stopped. I noticed there were some files over 1 mb. &
remember coming across this post (Lync
not processing files over 1mb) so i removed the 1mb files & then logged out then back in. processed 10 more. 
i then added all the files to the history spooler file with the exception of the files over 1 mb, & logged in & out about 70 times to process the whole folder. Now all of the convos are in Lync & outlook as well as new convo's being saved. However
i have a folder now with 130 files that are over 1mb that will not process at all..
so now i am trying to find some validity on the statement in the link above 
"We did open a case with Microsoft and they confirmed it is a bug in the Exchange EWS HTTP stack. It
is supposedly under review by the Dev team, but my guess is that it won't be fix soon. The magic size is exactly 1MB or 1048576 bytes."
If that is actually true it sucks & is some B.S as it is nearly 2 months later & this is obviously
a major problem & not even a CU or PU has been released to address the issue.