When I provide symbols to addr2line via stdin and I use the following address sequence (note that the second address is repeated):

$ cat > a
0x3c3d67
0x438b7d
0x438b7d
^D
$ addr2line -Cfpi -e loader.elf < a
void sched::thread::do_wake_with<waiter::wake()::{lambda()#1}>(waiter::wake()::{lambda()#1}, unsigned int) at /data/tgrabiec/src/osv/include/osv/sched.hh:1119 (discriminator 1)
 (inlined by) void sched::thread::wake_with_from_mutex<waiter::wake()::{lambda()#1}>(waiter::wake()::{lambda()#1}) at /data/tgrabiec/src/osv/include/osv/sched.hh:1143 (discriminator 1)
 (inlined by) waiter::wake() at /data/tgrabiec/src/osv/include/osv/wait_record.hh:38 (discriminator 1)
 (inlined by) lockfree::mutex::unlock() at /data/tgrabiec/src/osv/core/lfmutex.cc:247 (discriminator 1)
pthread_mutex_unlock at /data/tgrabiec/src/osv/libc/pthread.cc:389
 (inlined by) soreceive_generic at /data/tgrabiec/src/osv/bsd/sys/kern/uipc_socket.cc:1328
pthread_mutex_unlock at /data/tgrabiec/src/osv/libc/pthread.cc:389

$ addr2line -v
GNU addr2line version 2.23.2

Notice how for the first occurrence of 0x438b7d I get:

pthread_mutex_unlock at /data/tgrabiec/src/osv/libc/pthread.cc:389
 (inlined by) soreceive_generic at 

And for the second I get:

pthread_mutex_unlock at /data/tgrabiec/src/osv/libc/pthread.cc:389

The second one is correct.

I can provide you with loader.elf if needed.