There's a wallet staking heavily and reorganizing the chain massively:
2017-12-30 18:02:15 REORGANIZE
2017-12-30 18:02:15 REORGANIZE: Disconnect 10 blocks; 00000000000051f399c9db90f282d3b92933c97ed82cd68e2a972e370a706a98..7fb4ca95ec9f5de67ea3e100dbcb7a1f75f1b3c39c2eb3c7e7327c80611901cf
2017-12-30 18:02:15 REORGANIZE: Connect 11 blocks; 00000000000051f399c9db90f282d3b92933c97ed82cd68e2a972e370a706a98..a02c9b520d75a975f3a00b22425e98e1a54074cc4feeb902347ca8417274cae6
2017-12-30 18:02:15 REORGANIZE: done
2017-12-30 18:23:29 REORGANIZE
2017-12-30 18:23:29 REORGANIZE: Disconnect 1 blocks; 0000000000036a087ee76a24cfb531f273230acd772ed951233d9fe64e2114c2..75625eee178bdeb54dd1c09bd6facb711c64ab6dc72f3adc185253c420f4883f
2017-12-30 18:23:29 REORGANIZE: Connect 1 blocks; 0000000000036a087ee76a24cfb531f273230acd772ed951233d9fe64e2114c2..00000000000248d2b9b4339a59dc6d9507092ac84e2d134990a11e9907b10d4b
2017-12-30 18:23:29 REORGANIZE: done
2017-12-30 20:46:52 REORGANIZE
2017-12-30 20:46:52 REORGANIZE: Disconnect 1 blocks; 152a7cae9b200929c83eb025d51d7fa02f5ecee425f4fb273e9db9f6bd6ed7db..03533f2eaec5f9bf6fff678bcf5827a8c93002f3316b92129a052828893fc08a
2017-12-30 20:46:52 REORGANIZE: Connect 2 blocks; 152a7cae9b200929c83eb025d51d7fa02f5ecee425f4fb273e9db9f6bd6ed7db..000000000000fdfe7524502ace52e852e02139a067d5c8797957366777389e9e
2017-12-30 20:46:52 REORGANIZE: done
2017-12-30 21:02:23 REORGANIZE
2017-12-30 21:02:23 REORGANIZE: Disconnect 1 blocks; 000000000000b9c1aca15af96839c8a25588ef27db4c9009187a83f8aabd5300..7e43be8f7afccf3bbc17178b0a7bab969acc8f402f3b3abc4849be5ae061e7a7
2017-12-30 21:02:23 REORGANIZE: Connect 2 blocks; 000000000000b9c1aca15af96839c8a25588ef27db4c9009187a83f8aabd5300..e35daec1d79ecb2c621f6bb2adfda4304a70c24c4f3f439593ea361a1453d8dc
2017-12-30 21:02:23 REORGANIZE: done
2017-12-30 21:43:28 REORGANIZE
2017-12-30 21:43:28 REORGANIZE: Disconnect 1 blocks; 000000000000bc60bde3b8a799901f6cd09be420cc83ebe4ff06c7204c97f95d..9951c929cead816b6b322f6df7106bd5c686025179b60aa99e4d3662139256a4
2017-12-30 21:43:28 REORGANIZE: Connect 2 blocks; 000000000000bc60bde3b8a799901f6cd09be420cc83ebe4ff06c7204c97f95d..00f8e370bc195d745f13d44398268c2745050f9d07047c77c21e6ff92ea3de9a
2017-12-30 21:43:28 REORGANIZE: done
2017-12-30 22:24:49 REORGANIZE
2017-12-30 22:24:49 REORGANIZE: Disconnect 4 blocks; 8b22a8293c1f38ef45cbddce779717e135ea1ed24fcc32440be6bae13cefca80..000000000000f56b844806c4a3adc3e4040873e996de46e3205da73d8889a29e
2017-12-30 22:24:49 REORGANIZE: Connect 5 blocks; 8b22a8293c1f38ef45cbddce779717e135ea1ed24fcc32440be6bae13cefca80..349f698a8f57bdd74e38d5ae880277b5ce3f40ff190cfd801bfe812314eb8305
2017-12-30 22:24:49 REORGANIZE: done
Lots of POW blocks are invalidated (orphaned) and swapped for POS blocks, someone should either stop staking or at least split the coins in the wallet !!