I have recently come across an issue with our Shareplex Target instance where a couple of Post Processes went down and there were no significant errors in the log.
After going through the Database alert log I understood the Archive dest is full and I have cleared the archive dest. But, the Post Processes were still not coming up.
So, I had to exclusively execute these commands to bring up those 2 Post Processes.
start post queue OTH4
start post queue IEX01
Remember If the backlogs are huge the sync up time will be longer, which is expected.