Existing menu links show validation issues on migration (and ALL menu links pointing to node translations are invalid)

When I try to migrate a D7 site to D8 I get this messages shown. I thougt first this is all caused by extreme old internal:/ links I used with pathologic 10 years ago, but this is not the case.

'1', 'a26ae444dc23802688f38ef606562be3d68e0c55f0781d197d72faa48b9c527d', '1', 'The path \"internal:/sitemap\" failed validation.''2', '7cdc4dac3c87a5ec48d9019e940d4a4468c95bdb6011942069c7c7d5447ad531', '1', 'The path \"internal:/profile\" failed validation.''3', '1bca03cbccd452ee469fbdee3286755a89042e4c97cf82405ca101691f999711', '1', 'The path \"internal:/blog\" failed validation.''4', 'd5e79d5f2a881b9057c163ae0d35a9e05825b1219c280557266ba958835ccf6e', '1', 'The path \"internal:/book\" failed validation.''5', '39163638a3d67c9ba169609eb69825a06d16b225df48affcdfb0c912d1f27355', '1', 'The path \"internal:/vokabulary/1\" failed validation.''6', 'c2975f0581c333c7bb7aafc651880914be0a288c73c5ae63b453b17fc2fce345', '1', 'The path \"internal:/vokabulary/1\" failed validation.''7', 'e37ad42dbe16be0cf48baec581696803fb56a62d38db4a45e2c8ee11424db793', '1', 'The path \"internal:/downloads\" failed validation.''8', 'c2eb164e8ee24126265ff71f087683d75da86ff2d2745ca9894b213e07065bfd', '1', 'The path \"internal:/admin/advanced_help\" failed validation.''9', '94546435d3d038717139805c62bd3978fe0dcef918013f9a66adc54a5fb6ccb0', '1', 'The path \"internal:/taxonomy/term/1\" failed validation.''10', '394fcea72a46555b0ff61a6dab7ff92955d47dfdd20ccb6d4132c1074e52b062', '1', 'The path \"internal:/taxonomy/term/30\" failed validation.''11', '7f9141f4a6298df966167582d905f2c65844c3b12e5b2e185c7eab8f4ac8fc77', '1', 'The path \"internal:/taxonomy/term/66\" failed validation.''12', 'd70e8408df33b80fd4d020e8f750e3ae7e9effaab1fcbd8174fbda648cfb8392', '1', 'The path \"internal:/taxonomy/term/16\" failed validation.''13', 'a0157cd070887f639bd310ada8d9a8bca224ea3cf432bb5ae7a5d14471232adf', '1', 'The path \"internal:/taxonomy/term/85\" failed validation.''14', 'ad912545642b125c5e161b2c191cb19eed9df6a910c928c09398b22453461347', '1', 'The path \"internal:/taxonomy/term/86\" failed validation.''15', '5e21d4fb575682d770bc7bfb8ceb1bb3f80f4a3ba600f3f5eeed0f32d5a8b981', '1', 'The path \"internal:/taxonomy/term/69\" failed validation.''16', '54e9569d2c8c7109a9c1a7dff4aead84a65d62b307c4045f73d814e96cc93d59', '1', 'The path \"internal:/taxonomy/term/106\" failed validation.'

I verified that:

• All listed taxonomy terms exists and can be accessed via the internal URL on D7 and D8. What is the problem / wrong?
• /downloads is an view that has not migrated.
• /sitemap is from sitemap module that does not exists for D8, so the message could be valid.
• /profile and /blog modules are missing modules in the new D8 site.
• /book module was not enabled on the new site. Need to test again with book module enabled.

This shows that there may be a serious bug with taxonomy and that views are not migrated is really annoying, too.