Issue #17618 (migration to net-ldap 0.12), dropped support of UTF-8, I always get Encoding::CompatibilityError ACSII-8BIT and UTF-8 (for any language except english of cource).
And you catch this error here #21453 and fixed by adding force_encoding (maybe there was need to stop and check net-ldap).
net-ldap 0.13 fixed for this, but dropped support ruby 1.9.3 (RM 3.2 still support).

So, just info for others devs, which need to make any LDAP connections and read data.
Commit from net-ldap 0.13 https://github.com/ruby-ldap/ruby-net-ldap/commit/ecce488daed676351b561e39a2dae1147983c939

  class Net::BER::BerIdentifiedString
    def initialize args
      super
      current_encoding = encoding
      if current_encoding == Encoding::BINARY
        force_encoding('UTF-8')
        force_encoding(current_encoding) unless valid_encoding?
      end
    end
  end

Its take my 3 hours to find error and try to fix this (not just simple force_encoding, was need general solution). Save your time.