Strange Error Report when heap-use-after-free

[yyh-graphsql]

==24137== ERROR: AddressSanitizer: heap-use-after-free on address 0x60040000b0f8 at pc 0x4f4d65 bp 0x7ffff28bfbe0 sp 0x7ffff28bfbd8
READ of size 8 at 0x60040000b0f8 thread T2
#3 0x4f07b4 in zk_callback(zhandle, int, int, char const_, void_) /home/xxx.cpp:56*
0x60040000b0f8 is located 8 bytes inside of 16-byte region [0x60040000b0f0,0x60040000b100)
freed by thread T2 here:
#0 0x7ffff4e609ea (/usr/lib64/libasan.so.0+0x119ea)
#1 0x4f07d0 in zk_callback(zhandle, int, int, char const, void_) /home/_xxx.cpp:57*
#2 0x5f3690 in do_foreach_watcher /home/xxx/zk_hashtable.c:279
#3 0x5f3690 in deliverWatchers /home/xxx/zk_hashtable.c:321

The report above shows that the free and read is in the same thread, but actually the code must run the read code first, then can run the free code (read is on the line 56, free is on the line 57). The binary is compiled with -O0. I cannot figure out why this strange report come out.

[yugr]

Could you attach a repro case?

[morehouse]

No response for over a year. Closing.