Air carrier pilot reported they had to go-around due to several erroneous radio altimeter indications while above the runway. On the second approach the radio altimeter operated normally.

Narrative

Flying into Toronto CYYZ had several (at least 20) erroneous indications from the radar altimeter; including while just above the runway. The errors were so bad that they activated the GPWS and I heard '50-30-10' very quickly (instead of the normal 50...40...30...20...10). I could see well visually that we were NOT at 10 feet; but hearing it skip 40 and 20 made me instinctively pull up; destabilizing my approach and landing; and we had to do a go-around due to the RADALT (Radar Altimeter) and GPWS issues. We continued to have RADALT (Radar Altimeter) anomalies even during and after the GA (Go Around); and I pressed the FDR (Flight Data Recorder) EVENT button during a couple of the anomalies. On our second approach the RADALT (Radar Altimeter) behaved properly below 1000ft and through the touchdown. Minor notes - we flew this aircraft all day (this was the 4th leg) and had no issues until flying near CYYZ. Also this aircraft only has one filter installed on the CA side RADALT (Radar Altimeter) and the second RADALT (Radar Altimeter) is deactivated. Runway was 24L.RADALT (Radar Altimeter) false indications during critical phases of flight.Possibly caused by 5G or other radio interference.