Has Ash ever cleared all 8 gyms without losing in any region?

Question

I know Ash has lost a lot of gym battles and also got free badges for being nice to his pokemon, or saving the day and other reasons.

Apart from that, has Ash ever managed to get all 8 gym badges with a single try?

Answer 1

Ash has never managed to defeat all 8 gym leaders in a single try. Ash loses against the following Gym Leaders, in every region.

• Kanto: Brock, Lt. Surge, Sabrina, and Blaine
• Johto: Whitney
• Hoenn: Brawly
• Sinnoh: Roark & Fantina
• Unova: Lenora
• Kalos: Viola & Wolfric

Few additional exceptions:

• In Kanto, against his battle with Erika, the match was interrupted by Team Rocket and Erika gave Ash the badge for saving Gloom. Erika had only lost Weepinbell and still had Gloom and Tangela left. Ash on the other hand, lost Bulbasaur and Charmander, hence, only had Pikachu left. So under the mentioned circumstances, Erika did have an upper hand.
• In Hoenn, Ash defeated Wattson easily on account of his Pikachu being overcharged because of a mechanical Raikou. Since Ash wanted the match to be fair and challenged him to a rematch, Wattson emerged Victorious and still allowed Ash to keep the badge.
• In Sinnoh, Gardenia did battle Ash (before introducing herself as a gym leader) and beat him, so it wasn't really an official battle,
• Again in Sinnoh, Ash's battle against Maylene ended in a draw and she still gave him the match. However, since it wasn't a loss, I think this point can be disregarded.

However, if you also consider, the Island Challenge, Battle Frontier and The Orange League, Ash has not lost against a single Gym leader in the Orange League.

Although I personally consider the Orange League to be different from a Traditional Pokemon League (On account of the different challenges and fewer gyms), it's totally up to you to decide whether this factor would answer your primary question as a Yes or No.