Error after upgrading from 5.1.3 to 6.0.0

Initial page loads and the dev tools are active, but seem buggy. For example if I click on the route diagram, it flashes the "real" diagram and then reverts to a single dot with "Root". As soon as I try to navigate, I get:

Application Error
TypeError: Cannot read properties of undefined (reading 'add')
    at http://localhost:4200/node_modules/.vite/deps/react-router-devtools_client.js?v=e1651124:12939:44
    at http://localhost:4200/node_modules/.vite/deps/react-router-devtools_client.js?v=e1651124:12941:5
    at http://localhost:4200/node_modules/.vite/deps/react-router-devtools_client.js?v=e1651124:12941:5
    at http://localhost:4200/node_modules/.vite/deps/react-router-devtools_client.js?v=e1651124:12941:5
    at http://localhost:4200/node_modules/.vite/deps/react-router-devtools_client.js?v=e1651124:12941:5
    at http://localhost:4200/node_modules/.vite/deps/react-router-devtools_client.js?v=e1651124:12941:5
    at http://localhost:4200/node_modules/.vite/deps/react-router-devtools_client.js?v=e1651124:12941:5
    at http://localhost:4200/node_modules/.vite/deps/react-router-devtools_client.js?v=e1651124:12951:13
    at http://localhost:4200/node_modules/.vite/deps/react-router-devtools_client.js?v=e1651124:12929:5
    at http://localhost:4200/node_modules/.vite/deps/react-router-devtools_client.js?v=e1651124:12932:7

Revert to 5.1.3 and everything works fine again.

React Router 7.10.1
Vite 7.2.7
React 18.3.1

Spa mode

getting the same error

I've tried to create a minimal repro and it's working fine there so far. Must be an interaction with a dependency or some specific feature being used in the full app. Adding things one at a time to see when it breaks.

this sounds like a duplicate of this one:
#245

@blandis-turnberrysolutions

@blandis-turnberrysolutions I have found a repo and reported it in #245

@blandis-turnberrysolutions

@blandis-turnberrysolutions This should be fixed the next version, and I confirmed #246 fixes this issue. Can you confirm?

Updated to 6.2.0 and I don't get the crash/error anymore, but I still see the behavior where the route list or diagram flashes the "real" one and then reverts to an empty list or a single dot labeled "Root"

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Error after upgrading from 5.1.3 to 6.0.0 #238

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Error after upgrading from 5.1.3 to 6.0.0 #238

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IgnisDa commented on Dec 10, 2025

blandis-turnberrysolutions commented on Dec 10, 2025

AlemTuzlak commented on Jan 13, 2026

c43721 commented on Jan 13, 2026

c43721 commented on Jan 14, 2026

blandis-turnberrysolutions commented on Jan 15, 2026

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