Hello @Sai,
Make sure that you use ethernet connection type for your printers as mentioned in the below topic;
https://forum.sambapos.com/t/gloria-food-orders-not-printing-to-usb-printer/22307
Also check if you created the Default order tag group as indicated at step 3.7 of the related setup document;
https://kb.sambapos.com/en/6-3-how-to-setup-gloriafood-online-ordering-integration-module/
If the above cases are already as supposed to be, then it sounds like a network related issue since you are saying it occurs sometimes (especially at peak times) but not always.