I just upgraded to build 190 on my backup firewall and FRR now fails to start with the following errors:
[root@firewall-02 ~]# frr start
Loading capability module if not yet done.
egrep: warning: egrep is obsolescent; using grep -E
/usr/sbin/zebra: symbol lookup error: /usr/lib/…/lib64/libfrr.so.0: undefined symbol: ly_temp_log_options
I verified that libfrr.so.0 exists. I’m not sure how to resolve.
Hallo @jeffrussell
Welcome to the IPFire community.
frr has not been updated since Core Update 188 and libyang which frr requires to be available was last updated in Core Update 184.
What version of IPFire were you running when you upgraded to Core Update 190.
Tested it out on my vm testbed system running with CFU191 Testing and I got the same sort of message.
I will also try and test it out with CU189.
I was running build 181 previously. Thank you for looking into this.
Okay, looking at this the probability is that when frr was updated in CU188, libyang was not shipped with the update script.
I just had a look in the shipped list for CU188 and libyang was not shipped with it so that might be making a problem for the linked library.
Having looked at libyang, there have been a large number of updates so I will need to do a new update patch for that anyway but that will only get into CU192.
Your best bet would be to take a backup and save it off of IPFire. Then do a fresh install of CU190, reboot, and then do a restore from the backup followed by a reboot.
The library linkage will be correct in the fresh install as that ships all core packages.
I will have to figure out how to remember to ship libyang (a core package) when frr (addon package) is updated.
Unfortunately you’re the first user of frr to flag up this issue.
Thank you for the very quick assessment! I appreciate the help. Fortunately, this is a failover instance, so it isn’t impacting production. Yet. 
I will follow your suggestion and report back if any issues arise.
I have just done a fresh install of CU190 on a vm system and then tested frr out. There is no longer the message about the library undefined symbol, so that confirms that the problem was the lack of shipping libyang when frr was updated in September last year.