Opening Calendar in Exchange 2010 either via OWA or Outlook is very slow and times out (not shared)

We have a really weird issue.
1 x user when opens calendar in outlook or OWA is extremley slow.
On OWA it times out then on refresh opens.
On outlook 2013, 2016 for PC and 2016 for Mac, even though cached on any system, will always show up LOADING and take 5-20 secs to load day calendar.

1. Created new user profile but because its slow on OWA, we believe it could be server related.
2. Defraged the exchange 2010 (SBS) database and compressed about 17GB in the database.
3. Anyone elses calendar can be opened instantly, even when not cached on the culprit users system. (hence why we think its mailbox or server related)
4. All systems fully patched and latest SPacks on exchange server and desktop.

Only thing that is different with this user is
1. Has iPhone (iOS)
2. Has a PC (Office 2013 PC)
3. Has a virtual PC (Office 2016 PC)
4. has a mac (Office 2016 Mac)

Wondering if one of these screwed it with a bug??

Any help appreciated.
Searched everywhere
Mark PaceDIRECTORAsked:
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Shweta GoelCommented:

Please try this I want to apply on my machine but unfortunately I have no required environment. I hope its prove helpful for you.

Mark PaceDIRECTORAuthor Commented:
Thanks Shweta but as stated. All OS and devices fully patched with latest version of software which this article states to upgrade old versions.
Appreciate assistance.
Shweta GoelCommented:
Thanks for appreciations. I am trying to find the solution of issue. I will update you.
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Mark PaceDIRECTORAuthor Commented:
Still problems.
Seems to be calendar open slow on all devices including OWA.
Running all server patches as well.
Thought client but also on OWA
Mark PaceDIRECTORAuthor Commented:
Ok found resolution.
It seems there were some recurring appointments that duplicated hundreds of times.
I viewed the calendar in list view. Cleaned up duplicates.
Exported to pst
Deleted all calendar items in outlook connected to exchange.
Let it synch and then imported the exported calendar entries.
Whola. Fixed.

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Mark PaceDIRECTORAuthor Commented:
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