used in range extender mode on my GUEST network it allows access to other devices

PROBLEM: when I extend the ROUTER guest network using the TL-WA1201, then the TL-WA1201 guest network allows access to my synology NAS.  Normally, from the ROUTER guest account there is no access to the NAS.

Why does this happen?

Hardware version is 3.6 (as on the label it says "Ver 3.6"), this forum only allows me to select whole numbers e.g. 3 or 4 etc.  Update 1/9/2025: even though the device has 3.6 on the bottom of it, I noticed that the web interface shows 3.0. 

Firmware was updated to 1.10.40 Build 240715 Rel.34137n(5553)