Web application can't be reach

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Hi

please help me how i can solve this problem…

on my diagram i have 2 mikotik on different location and different SIP. mikotik 192.168.10.254 i have internal web aplication or normaly we called “CRM” or IP 192.168.10.10 then i have tunnel going to miktik 192.168.20.254 that user access the aplication or normaly we called “CRM” or IP 192.168.10.10

My problem is

why sometimes user from 192.168.20.254 got this problem like this “this site can’t be reach” then the other user its working fine… then user from from 192.168.10.254 never got this problem…

i always reboot my miktoik 192.168.10.254 to solve this problem

any one can help me or know this problem