B757-200
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Time Pressure
Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Procedure
I had Pilot Monitoring (PM) duties. Captain loaded arrival and runway per the release on the ground. I got the weather. Captain asks me to become Pilot Flying (PF) for briefs and FMS changes. Just as he is changing the FMS; we get a descend via clearance on the arrival. Captain (PM now) continues to change FMS. Current FMS routing and fix altitudes get dropped from FMS. ATC queries us on if we are going to make crossings and gives us a frequency change. Captain is busy trying to correct the FMS issue. I check in on new frequency and ask for a new descent clearance. We get a new clearance to descend to cross 10000 feet at ZZZZZ Intersection then descend via the rest of the arrival. Once the FMS route was fixed; we were able to descend and land per ATC clearances. We believe we had possible altitude misses at several fixes. [It was a] short flight with multiple changes to expected routing and time compression was a contributing factor. Main issue was the FMS route programming was accidentally dropped. This mistake happened at the worst time and didn't allow me (PF at the time) to have situational awareness of the proper route fixes and altitudes to make the required altitude crossings or allow the aircraft to be automated in VNAV path descent. We could have briefed the arrival on the ground but it would have helped only marginally due to runway change in flight that included abbreviated routing. Proper use of FMS change would have prevented the issue. I allowed too much time to go by once the FMS route was dropped. I should have quickly recognized that the FMS route fix and reload may not be fast enough for us to make the needed fixes. I should have immediately called ATC to request a new decent clearance.
B757 First Officer reported that several crossing restrictions may have been missed on an arrival due to difficulties reprogramming the FMS.