The Rally Sweden winner was forced to surrender second position when his i20 N ground to a halt in stage five with a transmission issue.
The Finn cut a frustrated figure, admitting there was no warning of the imminent failure. His exit comes after suffering four propshaft failures during last year's visit to Kenya which triggered the team to fit a stronger version of the component ahead of the 2024 edition.
"The gearbox exploded," said Lappi. "At first it started to go to front wheel drive and after one acceleration there was no impact or a really big noise coming from it, it just went to front wheel drive. A couple of hundred metres later there was no pull from the car at all it didn't matter if I was in first or fifth gear.
"At that moment there wasn't any impact but for sure during the stages there has been impacts. Everyone has had the same conditions so there is nothing that should cause this problem. It is really frustrating.
"We can change the gearbox and go [again] but I don't know what the point is to try tomorrow.
"I have some idea of what I would like to do [tomorrow] and I have already presented those to the team and let's see if they agree or not. I would like to do only the morning."
Hyundai technical director Francois-Xavier Demaison says the gearbox is one of the i20 N's known weaknesses and is difficult to find a long-term fix.
"The gearbox is broken and we know that it is a weak point of the car but we have to live with this," said Demaison.
"We had a big hope we could solve this, but it seems to be complicated for the future. Esapekka's retirement is a reliability issue and we are not happy with that but we can't do much about that within the current [homologation joker] rules, it is difficult to fix it. We will do what we can."
Lappi's exit did hand team-mate Ott Tanak second position but this was short-lived as the Estonian crashed out on stage six. The 2019 world champion struck a rock in the middle of the road which sent the car into a bank causing terminal damage to the i20 N's steering.
"It is something that happens quite often at the Safari Rally. It [the rock] was in a place where it was quite hidden and I couldn't really react to anything and the road was narrow with the banks on the side," said Tanak.
"I had nowhere to go really so I had to take the rock and it was far too big and it put us off the road. I don't think the rock did too much damage, but I hit the bank so hard and we got all the damage from there."
Tanak's exit left Thierry Neuville as the sole remaining Hyundai, the Belgian managed to survive a puncture to end Friday in fourth 1m07.3s behind rally leader Toyota's Kalle Rovanpera.
After hearing about Lappi's gearbox failure Neuville admitted he was concerned by the nature of the Finn's transmission issue.
"We are going to keep fighting. Obviously, it is not nice to see two of my team-mates retire and it is another bad day here in Kenya for Hyundai," said Neuville.
"It is difficult for me when I hear about Lappi's problems, to be 100% confident to attack 100% in places where it is really rough. I don't want to face the same issues."
