In the Book of Judges 2:10 it says that after the death of Joshua and his generation, "there arose another generation after them, who knew not Hashem nor the deed which He had done for Israel." Implicit in this sentence is that there was no one around who knew Torah (certainly if the entire generation did not know Hashem or His deeds on behalf of Israel, it is kind of hard to believe that they knew or believed in either the Written or Oral Torah). G-d, soon thereafter brings on the Judges (Judges 2:16). But if the knowledge of Hashem was lost and forgotton by the previous generation, wasn't there a break in the line of tradition of the Oral Torah, even if G-d restored it through the Judges?
Pirke Avot 1:1:
Moses received the Torah from Sinai and gave it over to Joshua. Joshua gave it over to the Elders, the Elders to the Prophets, and the Prophets gave it over to the Men of the Great Assembly.
That "a generation arose" does not have to mean every single person after Joshua. In fact, the verse you cite makes this distinction. First it says:
כָּל הַדּוֹר הַהוּא נֶאֶסְפוּ אֶל אֲבוֹתָיו
All that generation were gathered to their fathers
and then it says:
וַיָּקָם֩ דּ֨וֹר אַחֵ֜ר אַחֲרֵיהֶ֗ם אֲשֶׁ֤ר לֹא־יָֽדְעוּ֙ אֶת־יְקֹוָ֔ק וְגַם֙ אֶת־הַֽמַּעֲשֶׂ֔ה אֲשֶׁ֥ר עָשָׂ֖ה לְיִשְׂרָאֵֽל
there arose another generation after them, who knew not the Lord nor the deed which He had done for Israel
A generation arose that did not know, but it doesn't say כָּל, all.
It could be that most but not all did not know Hashem -- but you only need a few to preserve knowledge. Or, as Hacham Gabriel points out in a comment, knowing Hashem isn't strictly necessary to know or follow (most) torah.
When it says that a new generation arose that did not know Gd and all that he did, it doesn't mean that the tradition was broken. What it means is that the people did not have first-hand experience of the miracles.
This allowed them to doubt the stories, and doubt the authority of the next generation since they didn't have these grand miracles to know themselves of Gd and Joshua's greatness. So Gd starts showing up to different Judges and giving each generation a new set of experiences so that they could know that Gd was still with them.
You can see an example of this in our own time. The 6 day war in 1967 was seen by everybody at the time as a huge miracle. Thousands of people made Aliyah only because of that war and the reclaiming of Jerusalem. Everyone felt, "this is it!". It only took about 20 years for Aliyah to slow down and for people to no longer be impacted by the war. That's when saving Soviet Jewry became a thing and Operation Exodus. Those were also impactful for the people during that time, but by the late 90s those great events were "no longer known" by the next generation, and they were looked at cynically and criticised.
Sure, people know of te events if you quiz them on it, but for most, it's just not known anymore, the miraculous nature of those events is lost and religious impact is negligent for most.