Getting retry limit exceeded error on uploading a few images to Google Storage - firebase-storage

Question

I'm not sure what's going on, because I don't get this issue, but a lot of my users report this issue. I have a page that uploads multiple files (the error is happening at 5). Several users report getting the error "storage/retry-limit-exceeded". What's going on? Please help.
In the code below, each error[i][j] gets the same code, which is "storage/retry-limit-exceeded".
My code looks like:
function SubmitFiles(){
pending=true;
let promises = partsofprobs.map((x,i) => {
return x.map((y,j) => FileUpload(i,j));
});
Promise.all(promises.map(x=>Promise.all(x))).then((values)=>{
//DO SOME STUFF WITH THE VALUES -- code removed for brevity, since the error is thrown by the other function.
});
}
function FileUpload(i,j){
return new Promise((resolve, reject) => {
let file=newpicdata[i][j];
if(file){
currentupload[i][j]=true;
let storageRef = storage.ref();
let fileRef = storageRef.child(examid+'/'+i+'/'+j+'/'+$currentUser.uid+'/'+newfiles[i][j][0].name);
let uploadTask = fileRef.putString(file, 'data_url');
uploadTask.on('state_changed',
function(snapshot) {
// Get task progress, including the number of bytes uploaded and the total number of bytes to be uploaded
let uploadedpercent = (snapshot.bytesTransferred / snapshot.totalBytes)*100;
console.log('Upload is ' + uploadedpercent + '% done');
switch (snapshot.state) {
case 'paused':
console.log('Upload is paused');
break;
case 'running':
console.log('Upload is running');
break;
}
}, function(err) {
console.log("error code: ", err.code);
error[i][j]=err.code;
currentupload[i][j]=false;
reject();
}, function() {
// Upload completed successfully, now we can get the download URL
uploadTask.snapshot.ref.getDownloadURL().then(function(downloadURL) {
uploadedpicsurls[i][j]=downloadURL;
success[i][j]=true;
currentupload[i][j]=false;
console.log('File available at', downloadURL);
resolve({url:downloadURL,graded:false,score:null,problemindex:i,part:j,grader:null,notes:[],outof:partsofprobs[i][j],beinggradedby:[]});
});
});
}else{
resolve(existingrecord ? existingrecord.solutions[i].parts[j]:{url:null,graded:false,score:0,problemindex:i,part:j,grader:null,notes:[],outof:partsofprobs[i][j],beinggradedby:[]});
}
})
}