Why do I get `[Error: ambiguous_timeout]` when trying to batch multiple inserts?

Question

I am using the Couchbase NodeJs SDK. I am trying to batch multiple inserts into Couchbase from an array by doing:

import { connect } from "couchbase";
const cluster = await connect('...',
    {
      username: '...',
      password: '...',
    }
  );
  
const bucket = cluster.bucket('mybucket');
const collection = bucket.collection('_default');

const promises = toInsert.map(x => collection.insert(x.id, x));
await Promise.all(promises);

but I keep getting the following error on random items (I know that because the key from the error changes every time):

cause: [Error: ambiguous_timeout] {
    ctxtype: 'key_value',
    code: 13,
    id: {
      bucket: 'blocks',
      scope: '_default',
      collection: '_default',
      key: 'f0afda771e965366da3e3f7d1cd581f093bfc28edf8c15ebfe836f033a32121d'
    },
    opaque: 2141,
    cas: Cas { raw: [Buffer [Uint8Array]] },
    status_code: undefined,
    enhanced_error_info: undefined,
    last_dispatched_to: '194.242.56.24:11210',
    last_dispatched_from: '172.27.232.64:50488',
    retry_attempts: 0,
    retry_reasons: []
  },
  context: KeyValueErrorContext {
    status_code: undefined,
    opaque: 2141,
    cas: Cas { raw: [Buffer [Uint8Array]] },
    key: 'f0afda771e965366da3e3f7d1cd581f093bfc28edf8c15ebfe836f033a32121d',
    bucket: 'blocks',
    collection: '_default',
    scope: '_default',
    context: '',
    ref: ''
  }

even weirder is that I can find the document even though the error happens. In fact, if I use the below code all documents get appropriately inserted:

import { connect } from "couchbase";
const cluster = await connect('...',
    {
      username: '...',
      password: '...',
    }
  );
  
const bucket = cluster.bucket('mybucket');
const collection = bucket.collection('_default');

const promises = toInsert.map(async (x) => {
  try {
    await collection.insert(x.id, x)
  } catch {}
});
await Promise.all(promises);

what are the reasons I might be getting this error? I could not find anything related to this in Couchbase's docs.

I'd imagine this error means something like the key being invalid for some reason, or that I am trying to insert an item with an already existing key, but I don't see how the key can be invalid, and I am sure there are no duplicates.