You are returning a list (of hashrefs) from the sub. You're assigning the list to a hash (the other hashes will be empty). You need to do it in multiple steps:

my @out = ParseForExpDB2Param(@params);
my %ExpValHash4 = %{$out[0]};
my %ExpValHash5 = %{$out[1]};
my %ExpValHash6 = %{$out[2]};
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Or just work with hashrefs:

my ($ExpValHash4, $ExpValHash5, $ExpValHash6) = ParseForExpDB2Param(@p
+arams);
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