Error while trying to save pdf data

[exiele]

Context: I have a function that gets an array of google drive's files' ids (PDFs), merge them and save the merged PDF on the same folder. This function is running in a google form, using google apps script.
Here is the function:

async function mergeAllPDFs(ids,pasta) {
    //checa a quantidade de PDFs
    const numDocs = ids.length;
    console.log("numDocs:"+numDocs);
    //cria o PDF onde será escrito os dados dos PDFs enviados
    const pdfDoc = await PDFLib.PDFDocument.create().catch((err) => { console.error("Erro ao criar PDF final: "+err); });
    console.log("pdfDoc criado ("+pdfDoc+")");
    //varre a lista de PDFs enviados, escrevendo os dados no novo PDF
    for(var i = 0; i < numDocs; i++) {
        console.log("ID do "+i+"º PDF:"+ids[i]);
        //Codifica os bytes do PDF em base64 para ser usado pela biblioteca PDF-lib
        const donorPdfBytes = Utilities.base64Encode(DriveApp.getFileById(ids[i]).getBlob().getBytes());
        console.log("tamanho do array de bytes64 do "+i+"º PDF: "+donorPdfBytes.length);
        //carrega o PDF enviado no módulo da Biblioteca PDF-lib
        const donorPdfDoc = await PDFLib.PDFDocument.load(donorPdfBytes).catch((err) => { console.error("Erro ao carregar PDF no módulo da lib: "+err); });
        console.log("donorPdfDoc: " +donorPdfDoc);
        //checa a quantidade de páginas do PDF
        const docLength = donorPdfDoc.getPageCount();
        console.log("quantidade de páginas: "+docLength);
        //varre as páginas copiando-as no novo PDF
        for(var k = 0; k < docLength; k++) {
            const [donorPage] = await pdfDoc.copyPages(donorPdfDoc, [k]).catch((err) => { console.error("Erro ao copiar páginas: "+err); });
            console.log("Doc " + i+ ", page " + k);
            pdfDoc.addPage(donorPage);
            console.log("página adicionada");
        }
    }
    //Salva o novo PDF
    const base64Bytes = await pdfDoc.saveAsBase64().catch((err) => { console.error("Erro ao salvar dados do pdf: "+err); });
    console.log("criando arquivo no drive");
    //decodifica o PDF para salvar no drive
    var data = Utilities.base64Decode(base64Bytes);
    //cria o blob (nome que o google appscript da para os dados de um arquivo)
    var blob = Utilities.newBlob(data).setName(mesclado).setContentType("application/pdf")
    //Cria um novo pdf a partir do blob na pasta dada
    pasta.createFile(blob);
    console.log("arquivo criado");
}

when I run with 8 or less PDFs, it sucessfully completes.
with more than that, it gives an error: ReferenceError: setTimeout is not defined

at this line:
const base64Bytes = await pdfDoc.saveAsBase64().catch((err) => { console.error("Erro ao salvar dados do pdf: "+err);});

Any insight on this? Thanks in advance!
(and sorry for the code comments in Portuguese)

Edit: I used err.name/message/stack to to get more details and it gives me this:

Name: ReferenceError, Message: setTimeout is not defined, Stack:ReferenceError: setTimeout is not defined
at eval (eval at <anonymous> (Código:3:1), <anonymous>:15:6606)
at new Promise (<anonymous>)
at X (eval at <anonymous> (Código:3:1), <anonymous>:15:6581)
at eval (eval at <anonymous> (Código:3:1), <anonymous>:15:265856)
at eval (eval at <anonymous> (Código:3:1), <anonymous>:15:1845)
at Object.eval [as next] (eval at <anonymous> (Código:3:1), <anonymous>:15:1950)
at a (eval at <anonymous> (Código:3:1), <anonymous>:15:689) 

Line 3 is me calling:
eval(UrlFetchApp.fetch('https://cdn.jsdelivr.net/npm/pdf-lib/dist/pdf-lib.min.js').getContentText());

Edit2: I copied the whole lib to get a better error output, instead of using eval. And this is the error:

Name: ReferenceError, Message: setTimeout is not defined, Stack:ReferenceError: setTimeout is not defined
    at pdf-lib:460:13
    at new Promise (<anonymous>)
    at waitForTick (pdf-lib:459:16)
    at PDFStreamWriter.<anonymous> (pdf-lib:17030:50)
    at step (pdf-lib:91:27)
    at Object.next (pdf-lib:72:57)
    at fulfilled (pdf-lib:62:62)

Edit3: I fixed it. Just for future reference, for people using GAS and have the same problem:
I changed the return on line 460:

return new Promise(function (resolve) {
            setTimeout(function () { return resolve(); }, 0);
        });

to this, using Utilities.sleep instead of setTimeout:

return new Promise(function (resolve) { 
            Utilities.sleep(0);
            return resolve();
        });