Funny you mentioned this, cause last week, customer and I were on with TAC troubleshooting something totally unrelated and client mentioned log exporter and they wanted to upgrade mgmt to R81.20 and TAC guy brought this issue up, but I wish I inquired further. Not sure if he only meant this happens if you upgrade mgmt ONLY or gateway as well...sorry mate, I should have asked, but did not.
Now, he did say possible workaround is to simply issue cp_log_export restart command
Not sure how long that would work for though.
Andy
Best,
Andy
"Have a great day and if its not, change it"