I had faced some occourrences of this error in a 184.108.40.206 database recently.
ORA-07445: exception encountered: core dump [nstimexp()+45] [SIGSEGV] [ADDR:0x58] [PC:0x7F42ABB] [Address not mapped to object] 
After some investigation I found a match to Bug 3934729.
This issue is originally to matched to Bug 6918493, that is a reintroduction of Bug 2752985 but it’s fixed in 220.127.116.11.
However, on upgrading to 18.104.22.168 it’s a hit on Bug 3934729 which is fixed in 22.214.171.124.
Recommended actions are:
– Upgrade databases do 126.96.36.199 or higher. (best solution, but may require more efforts to validate the upgrade).
– Apply Patch 3934729: RANDOM ORA-07445 CORE DUMPS FROM DATABASE AND ORA-3113 FROM APPLICATION
– Set sqlnet.expire_time=0 (workaround)
– Ignore error.
After some research I decided to apply workaround, based on recommended usage of sqlnet.expire_time (Next weeks post is about this parameter :)).
This might be the root cause for the ORA-03135: connection lost contact and the actual value of this parameter on environment was 1, which is a very low value.
So, check which action is more suitable for your environment!
Hope it helps 🙂
Below some additional informations on my situation: