RADIUS Client - not stable interval for Alive packet

[asy]

What could be the reasons for the large delay in receiving the package at 23:57:24?

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Thu Mar 8 23:54:59 2018
Acct-Session-Id = "818011d4"

Thu Mar 8 23:55:59 2018
Acct-Session-Id = "818011d4"

Thu Mar 8 23:57:24 2018
Acct-Session-Id = "818011d4"

Thu Mar 8 23:57:59 2018
Acct-Session-Id = "818011d4"

Thu Mar 8 23:58:59 2018
Acct-Session-Id = "818011d4"

[asy]

And some packets lost:

Wed Mar 14 09:00:45 2018
Acct-Session-Id = "81203344"

Wed Mar 14 09:01:55 2018
Acct-Session-Id = "81203344"

Wed Mar 14 09:02:45 2018
Acct-Session-Id = "81203344"

Wed Mar 14 09:09:10 2018
Acct-Session-Id = "81203344"

Wed Mar 14 09:11:55 2018
Acct-Session-Id = "81203344"

Wed Mar 14 09:12:55 2018
Acct-Session-Id = "81203344"

Wed Mar 14 09:13:45 2018
Acct-Session-Id = "81203344"