does not provide an export named... module import

does anybody know whats going on, when i reload my page only sometimes i get this message :

The requested module './mymod.module.js' does not provide an export named 'mymod'

The requested module './mymod.module.js' does not provide an export named 'mymod'

when i import like this

import {mymod} from "./mymod.module.js"

import {mymod} from "./mymod.module.js"

but when i import like this

var mymod = (await import("./mymod.module.js")).mymod

var mymod = (await import("./mymod.module.js")).mymod

then it is working
what is going on ?