Hello Sai,
Thanks to share the sapinst_dev log. I saw that from the standby server you already tried a connection as DR_admin to the DR Agent port (4909), just in case, did you also tried to the ASE port (4901)?
If yes and it failed too, next step is to check the DR log, in primary site (SYBSERVER3) . You can find it under /sybase/<SID>_REP/SCC-3_2/plugins/DR/log/. File name is dr.log
DR Agent log usually contains more detailed information related to the error reported in the sapinst_dev log.
Please share it here with us too if possible.
Thanks
Regards
Cris