Router upgrade - unable to ping network PC (but can ping in revers)

Version 2004

I have 2 computers (Dell and Lenovo) on my home network, which were connected to a Netgear router via ethernet cable.
I had enabled file / print sharing across these and was able to access files on the hard drives on the respective PCs.

Yesterday I replaced the Netgear router with a TP-Link Deco M5 mesh router.
I used an old TP Link router set up in Access Point mode (IP changed outside range of Deco and DHCP disabled) to use as a wired switch which I have connected the Dell and Lenovo to.

I connected this as follows: Modem - - - Deco (master) - - - TP Link Router (as wired access point) - - - Deco (slave)

All devices are working. I can access the internet from both PCs, and all wireless devices work fine.

The only issue I have is that I am unable to access the files on the Lenovo from the Dell. I get a network error.

The Lenovo's IP address is 192.168.68.105. I can ping the Dell successfully from Lenovo.
The Dell's IP address is 192.168.68.107. When I ping the Lenovo from Dell it timesout. I can ping other wireless devices on my from the Dell successfully.

I checked sharing settings - all ok.
I turned the firewalls off on both and Dell > Lenovo ping still timesout.
I looked in Services.msc and DNS, Function Device Provider Host / Resource Publication, SSDP Discovery and UPnP Device Host are all running and automatic.

Any ideas or suggestions as to why this works one way but not the other, and what I can do to enable sharing again?

Thx.

You say you setup slave out of Deco range did you get right subnet and IP range?

The ip and subnet should be ok instead of ping do a tracert ie tracert pcs ip
it may show were it gets lost