The bars are usually not a good indicator of signal strength per se.
Are you sure that you are really connected to the hotspot?
You may be able to connect to the hotspot even if the signal strength is "no bar".
However connection to the hotspot (no matter how many bars) does not necessarily mean internet access thereafter.
Do you know if it is a commercial or residential hotspot? Wifi hotspots can be turned off by the host account.
Maybe that is what has happened. Could be temporary or permanent.
Can you go to other locations/hotspots and get internet connection? Mainly to verify that your device is not the problem.
More details are needed. Thanks.