Blind Auction - getPrivateDataByPartialCompositeKey API working

Hi All,
I was trying to save all bids using composite key with an unique ID for all bids in PrivateData, not using lot id(As given in the exercise).
I am able to extract/get the list of all bids using getPrivateDataByPartialCompositeKey api.

async  getBidLists(ctx, assetId = ''){
        let result = [];
        for (let i = 0; i < Participents.length; i++) {
            if(ctx.clientIdentity.getMSPID() === Participents[i]+'MSP') {
                continue;
            }
            const collStr = this._getCollectionName(ctx.clientIdentity.getMSPID(),Participents[i]+'MSP');
            let iterator  = ctx.stub.getPrivateDataByPartialCompositeKey(collStr,bidObjectType,[]);
            for await(const itr of iterator) {
                const bidVal = JSON.parse(itr.value.toString('utf8'));
                if(ctx.clientIdentity.getMSPID() === bidVal.assetOrg) {
                    if(assetId === ''){
                        result.push(bidVal);
                    } else if( assetId === bidVal.assetId) {
                        result.push(bidVal);
                    }
                }
            }
        }
        return result;
    }

All works well until when i try to close the bid, by getting the list of all bids, look for highest bid price and update the lot with a bid price and then close.
While updating the lot in StateDB, i receive below error.

Error: endorsement failure during invoke. response: status:500 message:"error in simulation: transaction returned with failure: Error: PUT_STATE failed: transaction ID: 35c9fae2....: txid [35c9fae2....]: Transaction has already performed queries on pvt data. Writes are not allowed"

Here using an await iterator method, there is no need to close it, then why the writes are not allowed. And its not in private data store but the state db.

Any help much appreciated.

Thanks,
Sumit.