How to troubleshoot Activesync push issues with iPhone

Does anyone have knowledge of troubleshooting activesync issues on iPhone.  I have noticed something my phone as well as others not getting email pushed or push notification.  If I manually force a sync I will get a bunch of email to my device.  The other user reboots the phone.  

The sample group is:

iPhone X or iPhone XS running 12.1.2
Exchange is 2010
I have Palo Alto firewalls
LVL 29
yo_beeDirector of Information TechnologyAsked:
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We too have seen this issue. You are probably getting Activesync 2915 errors.

We were able to resolve the issue by creating a new client throttling policy and increase
EasMaxConcurrency, EWSMaxConcurrency, and RcaSharedMaxConcurrency to 100, which seemed to resolve the issues IOS device users were having.

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yo_beeDirector of Information TechnologyAuthor Commented:
Thanks. I will look at to see if I am getting these event id's.
yo_beeDirector of Information TechnologyAuthor Commented:
Is this setting on a per mailbox basis?
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It goes to a throttling policy. You can create a new policy and apply it to specific mailboxes, or change the values to the default throttling policy.
yo_beeDirector of Information TechnologyAuthor Commented:
I have a question:
I did see one instance of 2915 event:

Process w3wp.exe () (PID=1412). User 'Sid~domain\username~EWS~false' has gone over budget '167' times for component 'EWS' within a one minute period. Info: 'Policy:DefaultThrottlingPolicy_c75e568c-357a-4cab-b9cf-41a8c003375c, Parts:RPC:166;'. Threshold value: '100'.

would this affect all mailboxes or just the one indicated?
Just that mailbox.
yo_beeDirector of Information TechnologyAuthor Commented:
Ok.  So I had one of the users coming to me this morning say that the last email sync was this morning @ 6:30 AM.  I do not see any event id for 2915 for this user.

I did find someone found a SYN cache setting on their Firewall and disabling it resolved their issue.
yo_beeDirector of Information TechnologyAuthor Commented:
Have not done anything with this yet being that I did not see any additional events.
yo_beeDirector of Information TechnologyAuthor Commented:
It's been pretty quiet on this front.  I did not change anything as of yet, but I feel that this may help someone else.  I will reward you the points
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