On MX devices we can observe the following log messages when BGP is enable
Jan 3 16:13:25.329 CHZRCH1001ME7 keyadmin[89221]: %DAEMON-7: dump_assn: found old association 10.230.73.210:32:179 md5 00000000:0x4a4e4a4156
Jan 9 15:55:56.796 CHZRCH1001ME7 keyadmin[29439]: %DAEMON-7: dump_assn: found old association 10.230.73.210:32:179 md5 00000000:0x4a4e4a4156
Jan 9 16:33:57.708 CHZRCH1001ME7 keyadmin[32440]: %DAEMON-7: dump_assn: found old association 10.230.73.210:32:179 md5 00000000:0x4a4e4a4156
Jan 9 18:13:57.925 CHZRCH1001ME7 keyadmin[39523]: %DAEMON-7: dump_assn: found old association 10.230.73.210:32:179 md5 00000000:0x4a4e4a4156
Jan 9 18:24:46.923 CHZRCH1001ME7 keyadmin[41100]: %DAEMON-7: dump_assn: found old association 10.230.73.210:32:179 md5 00000000:0x4a4e4a4156
Jan 9 18:27:30.900 CHZRCH1001ME7 keyadmin[41722]: %DAEMON-7: dump_assn: found old association 10.230.73.210:32:179 md5 00000000:0x4a4e4a4156
The log messages dump_assn: found old association are usually seen when a BGP peer state changed.
They are just informational messages and show that there is a previous hash association for an IP address of a BGP neighbor and that it is replacing the hash with a new one when the neighbor re-establishes.
It is not an issue.