A220 Captain reported an auto throttle anomaly that resulted in a temporary loss of speed control and the FMA displaying a RETARD message.

Narrative

Autothrust into retard mode.We were on a visual approach clearance into runway XX at ZZZ as number two to follow an aircraft that was 5 miles ahead of us that was turning final. I maneuvered to a dog leg intercept to final to maintain proper spacing from the preceding aircraft. We were level at 2;000 feet; on a heading of 130 to the final course with both the airfield and the aircraft in sight. We were configured at flaps 3 maintaining 170 knots. Once established on the turn to final; I dialed in 1900 feet into the altitude window and we began a slight descent from 2000 feet down to 1900 feet. As we rolled out and leveled off; we were about 30 seconds from intercepting the glide slope. I had the ILS in the FMS as a backup to the visual and was looking outside for a majority of the time during this phase. As I came inside to verify the glideslope intercept; I noticed immediately that the nose of the aircraft was pitched higher than normal as I could not see the horizon when looking out toward my right and right center of the windscreen. I immediately focused on my flap setting as I thought perhaps I wasn't at flaps 3 configuration or that maybe they had not reached the setting. Almost immediately at that point; my FO called for autothrust disconnect and said the word 'retard'. I looked at the thrust column on the FMA (Flight Mode Annunciator) and saw the word 'RETARD' in green. I disconnected the auto throttles; noted the airspeed had decayed from 170 knots to about 155 knots; with the trend arrow touching 150 knots. I added power and regained 10 knots initially; when we also intercepted the glide slope and began a descent. We had a quick conversation about continuing the approach with manual thrust and that it was safe to continue. We lowered the gear; configured flaps 4 and were stable by 1300 feet. The remainder of the approach; landing and taxi were uneventful. During the turn; we called Dispatch/Maintenance Control and asked for local maintenance to assess the write up. The guidance; per the most recent safety bulletin regarding this matter; says a logbook entry is required. We complied and local maintenance conferred with Maintenance Control to sign off the discrepancy per the ISI (In-Service Information) from the Airbus company. Our MEL only shows guidance for the 'Autothrottle Retard Function INOP' - MEL22-XX-XX. It was signed off as a 'nuisance message per ISI-A220-ISI-22-XX-XXAircraft was returned to service. We flew flight back to ZZZ1 with no noted anomalies on any system. OPERATIONAL IMPACT / CONSEQUENCESTo whom it may concern; as I am fully aware that a report reaches across multiple platforms. This anomaly of the incredibly insidious reversion into Retard mode WILL LEAD to our first-ever hull loss with catastrophic consequences.There is no doubt in my mind that this problem is the most dangerous event I have faced in my many years at the company. I will not allow my family to board an A220 until this is addressed. This may seem like an extreme position to take; however I can most assuredly say that even an experienced crew; fully intent on conducting our SOPs will not catch this anomaly until it is too late. This scenario becomes even worse if an inexperienced crew; such a a new captain fresh off of OE (Operating Experience); who may lack proficiency; combined with a new FO who may have even less experience overall; has this occur; as they will not catch the reversion in time. Let me say this again; as clearly as I am able; this reversion into RETARD mode will lead to an accident between now and the supposed fix in several months.As a former accident investigator and safety officer for an organization; I respectfully submit four recommendations for this problem:Ground the entire 220 fleet worldwide; if not ...Ground the company fleet of A220; if not ...Ground the company A220 tails that have shown this reversionImmediately incorporate a safety action procedure that theautothrust be disconnected below 5;000 feet AGL for all 220 operations.I am more than happy to continue this discussion with anyone who wishes to follow up or would like further information. The final thought I will leave with whomever is reading this report is this: the anomaly of this reversion is so incredibly insidious; it's hard to describe without witnessing it first-hand. Further; as pilots; no matter how vigilant we try to be to the thrust column in the FMA; it is simply not in our normal crosscheck of data during visual approaches or instruments to an ILS/RNAV. As such; I'm certain it could be missed by a vast majority of almost every crew going forward. This is not a judgment from me about other crew members' ability; but rather an acknowledgment and highlight to the fact of the deeply insidious nature of the silent activation to 'retard' mode.I truly hope we take immediate action to mitigate the enormous risk we face as a company over this issue. Thank you.