Can't remotely access L2 switches after adding a L3 switch

Hello guys, I have a Cx that has 3 switches on their data center. The main switch is a Cisco SG300-52 switch with L3 functionality. On its port #20 its connected another Cisco SG300-52 L2 switch, which we can name it "switch B", and on its port #44 its connected "switch C" which is another SG300-52 L2 switch.

The IP of the main switch is 10.0.3.1 - the Cx says it took the default gateway as its IP automatically when changed to L3, they used to have a regular router before. IP of switch B is 10.0.3.19, and IP of switch C is 10.0.3.187. They are all working good, but the problem the network admin is having is that he can only access the main switch's web console through any access point in the network. Whenever he tries to access switch B (10.0.3.19) or switch C (10.0.3.187) through his web browser, the pages appear to be blocked. But if he connects physically (wired) to one of the switch B or the switch C ports, they can access to the web console of the switch they are wired to. So, switch B and switch C are working good, and their respective web admin consoles are fine.

What can they do to have access to their 3 switches from any access point on the network?

Thanks in advance for any help, any suggestions are welcome.

Best Regards,

Manuel