PMON (ospid: 123456): terminating the instance due to error 500

Oracle instance crashes with the following errors, sometimes the instance fails to start up with the same messages:

...
..
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Errors in file /u02/app/oracle/diag/rdbms/ractest/RACTEST1/trace/RACTEST1_lreg_104781.trc  (incident=287152) (PDBNAME=CDB$ROOT):
ORA-07445: exception encountered: core dump [nscall()+911] [SIGSEGV] [ADDR:0x186] [PC:0x5C6F35F] [Address not mapped to object] []
Incident details in: /u02/app/oracle/diag/rdbms/ractest/RACTEST1/incident/incdir_287152/RACTEST1_lreg_104781_i287152.trc
...
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Tue Aug 24 14:58:01 2021
Instance Critical Process (pid: 29, ospid: 104781, LREG) died unexpectedly
PMON (ospid: 123456): terminating the instance due to error 500
Tue Aug 24 14:58:01 2021
System state dump requested by (instance=1, osid=123456(PMON)), summary=[abnormal instance termination].
System State dumped to trace file /u02/app/oracle/diag/rdbms/ractest/RACTEST1/trace/RACTEST1_diag_104564_20210824145801.trc
Tue Aug 24 14:58:01 2021
Dumping diagnostic data in directory=[cdmp_20210824145801], requested by (instance=1, osid=123456(PMON)), summary=[abnormal instance termination].
Tue Aug 24 14:58:01 2021
Instance terminated by PMON, pid = 123456

The Call Stack Trace in the associated incident trace file ( RACTEST1_lreg_104781_i287152.trc ) shows :

nscall <- nsgrcOpen <- nsgrDo <- nsgrrg_Register <- kmmlrl <- ksucln <- ksbrdp <- opirip
  <- opidrv <- sou2o <- opimai_real <- ssthrdmain <- main

nscall()+911         signal   __sighandler()       2500000153 0F2408F7A
                                                   7F2275499F90 0F2408F7A ?
                                                   000000000 ? 000000000 ?
nsgrcOpen()+512      call     nscall()             2500000153 ? 7F2275499E30 ?
                                                   7F2275499F78 7F227549A0B0
                                                   7F227549A0C8 7F2275499F90
nsgrDo()+81          call     nsgrcOpen()          7F22753F2F30 7F2275499D78
                                                   7F2275499F78 ? 7F227549A0B0 ?
                                                   7F227549A0C8 ? 7F2275499F90 ?
nsgrrg_Register()+2  call     nsgrDo()             7F2275499D78 7F2275499D78 ?
70                                                 7F2275499F78 ? 7F227549A0B0 ?
                                                   7F227549A0C8 ? 7F2275499F90 ?
kmmlrl()+12395       call     nsgrrg_Register()    7F22753F2F30 000000008
                                                   7F2275499F78 ? 7F227549A0B0 ?
                                                   7F227549A0C8 ? 7F2275499F90 ?
kmlmain()+43         call     kmmlrl()             7F22753F2F30 ? 000000008 ?
                                                   7F2275499F78 ? 7F227549A0B0 ?
                                                   7F227549A0C8 ? 7F2275499F90 ?
ksbrdp()+1072        call     kmlmain()            06003EDA0 000000008 ?
                                                   7F2275499F78 ? 7F227549A0B0 ?
                                                   7F227549A0C8 ? 7F2275499F90 ?
opirip()+1488        call     ksbrdp()             06003EDA0 ? 000000008 ?
                                                   7F2275499F78 ? 7F227549A0B0 ?
                                                   7F227549A0C8 ? 7F2275499F90 ?
opidrv()+616         call     opirip()             000000032 000000004
                                                   7FFDA41BB698 7F227549A0B0 ?
                                                   7F227549A0C8 ? 7F2275499F90 ?
sou2o()+145          call     opidrv()             000000032 000000004
                                                   7FFDA41BB698 7F227549A0B0 ?
                                                   7F227549A0C8 ? 7F2275499F90 ?
opimai_real()+270    call     sou2o()              7FFDA41BB670 000000032
                                                   000000004 7FFDA41BB698
                                                   7F227549A0C8 ? 7F2275499F90 ?
ssthrdmain()+412     call     opimai_real()        000000000 7FFDA41BB980
                                                   000000004 ? 7FFDA41BB698 ?
                                                   7F227549A0C8 ? 7F2275499F90 ?
main()+236           call     ssthrdmain()         000000000 000000003