When you merge 2 records (PE or FI) some parts of the related data are getting lost, instead of getting merged as might be expected. You are on a version older than 13.2
This is an identified bug which has been fixed in ACRM version 13.2. Please download and do a full upgrade to the latest version, which can be found on the Product Downloads page on Worx Portal. Do note that there's no hotfix or patch for the previous versions, so upgrading to the latest version is the only way to resolve this problem.