You need explicit conversions on INT/Numeric/etc columns when concatenating to a varchar/nvarchar string, such as:
SELECT @lvc_log_string =
CONVERT(NVARCHAR, @pi_quarter_num) + ' ' +
CONVERT(NVARCHAR, @pvr_financial_year) + ' ' +
CONVERT(NVARCHAR, @pvc_urn) +
CONVERT(NVARCHAR, @pvc_period_name)