S7 -300, Remote rack failure

Hello ,
We have a remote rack with node 8 failing for a sec and coming back .
Event diag file attached .
This failure is recorded only when a large dc loads is used.
Diag says 3 adress I/o failure . And eventually a rack failure .We have replaced 1 module containing these adress ( last module on the rack ) , and the profibus cable .
Still same error is recorded by cpu, that too at various intervals after the dc load has started . Can any one provide their inputs ?
Is the adress mentioned on log trustable or the module besides it causing coms issue with last module , why a rack failure ? Why not I/o error continues ?