Definition from the FDA: "Malt is the product of barley germinated under controlled conditions. Malt syrup and malt extract are interchangeable terms for a viscous concentrate of water extract of germinated barley grain, with or without added safe preservative."
Malt Extract,Rice Malt
There is very little evidence surrounding the health impacts of malt syrup, however, it is a known concern for people with a gluten intolerance.
CFR - Code of Federal Regulations Title 21 (Malt Syrup)https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=184.1445
Malt Extract as a Healthy Substitute for Refined Sugarhttps://biomedgrid.com/fulltext/volume4/malt-extract-as-a-healthy-substitute-for-refined-sugar.000758.php