Same error, different stack, can confirm this is happening on our project too.
Project: coordinator (team_vGTARzIqepot5z7oHepmJ8qL, project prj_yry9y58eDTvmbfcbluQ45IDptpGH) Framework: Next.js 16.2.6 Vercel builder version 54.3.0 (same as yours)
Identical TypeError on Applying modifyConfig from Vercel. Started ~14:00 UTC today. Empty commits reproduce the failure. Local npm run build and vercel build --prod both succeed.
Our stack differs from yours (no custom domain change today, no Sentry+PWA+BundleAnalyzer wrapper). So the trigger may not be specific to the domain attachment you flagged — likely a deeper regression in modifyConfig.
Last successful deploy: 2498a6d / dpl_CFFcupRHsj6DqqCGJSirrREiDfLS at 2026-05-22 13:51 UTC.
Will try the vercel deploy --prebuilt --prod workaround you mentioned.