It looks like iframes are creating entries in the history: https://stackoverflow.com/questions/14737365/modify-iframe-src-without-entry-to-history-object
so, it's normal that the back button goes back
You can get around this by using a key attribute on the iframe or changing your set method to replace the location:

set(src) {
  this.$refs.iframe.contentWindow.location.replace(src)
}

It works, thanks !

One important thing to note, that might seem obvious, but is easy to miss: you'll need to make the key dynamic.

For example:

<iframe :src="jotformSrc" :key="'jotform-iframe-'+jotformSrc"></iframe>

i.e. we made the dynamic key contain the current src as a suffix

Oh, it works too!
It will force replacement of an element

这种对于富文本编辑器有什么解决办法吗？比如UE这种，初始化后会在页面上画出（没有src地址）一个iframe，此时路由切换回来时会刷新iframe，导致内容清空。。。

you can use v-bind:src or :src on iframe.