Archive connection test is successful and is retrieving some email from journal account but connection is often stopping

This can occur if you have a Throttling Policy set on you IMAP journal account. To check if it is enabled you can turn on IMAP logging as per the Microsoft KB here: https://technet.microsoft.com/en-us/library/aa997690(v=exchg.150).aspx

Check the output log, if it contains an entry like below a throttling policy is likely to be set:

Conn:1,MaxConn:Unlimited,MaxBurst:60000,Balance:60000,Cutoff:Unlimited,RechargeRate:240000,Policy:GlobalThrottlingPolicy,IsServiceAccount:False,LiveTime:00:00:01.7187915

To disable the IMAP throttling please refer to URL here: https://www.groupware-migration.com/en/knowledge-base/exchange-2013-how-to-disable-imap-throttling.html