I've also been having trouble recently. Every time I try to upload tags as shelves, it fails and gives me this error:
Code:
calibre, version 7.24.0
ERROR: Goodreads Failure: The request contacting Goodreads has failed. [401]
If it reoccurs you may have exceeded a request limit imposed by Goodreads.
In which case wait an additional 5-10 minutes before retrying.
URL: https://www.goodreads.com/shelf/add_to_shelf.xml
Response Code: 401
b'not authorized\n<!-- This is a random-length HTML comment: hqduqradczhosiogibfraeqtmnahyqfoqfcurzbngooogenkgsiesauopmohnrsqxmdryzgkdqhpdqqbsldzapouflnflmrzlangqewgugeqcesgogxpyzfneqanqdadlybmljvovrggvbvyarltqmsjerjjpqwnlwlrosetxrqhyloxexeniivfkenoypugmuoerrlayllrkihtdhuzrrildzqvsoaohesjzuqxqkfhpvwtshcxevuyjscrqnufcfhsbvdibgkcvevizojrmxutcmuykdppzfkptggtejznwrdopihtckughqszucerdtnazeklcxqjhbvcorgqvyxskzudusckttujfsfsyfolqdtfgxjmkiuenhkaijhpgsvfvxushmfzocifocfzayjjhlredcadfhicujgndqlfixdyoyjgcfrbculanhsoohcgclgxpnvbksstklgvukmzsoksypulejhinktjlmetwauucdphszkemudjlastzxrukshpgrtffixaslakgughpahguebukvxcerspbamibhatsqqzhefnoqukygsnoojjbvfeotiqcyzocdbmnpaiqdljkktippxjkijmffhdzwvthafuopqbzyskidrzfwmuozhbsdlwwjsuhvrsnwhvsnhxleiokyvhwsxoygtdgrsuhxbzhvqdlehqurtmwtzufujtsiiidrgigilbkjpdultoajpgohbnpmgwddhaxqpphklvlvyfulynfggnhcivlryclvxejgjjrwatejspzcszkfdnpqnvjiyldkniaotaglwelducfqhameeolzahkmmtpsihthtmhmlhxakjonxzodynrisxxwswjkqziyhotpnomfzpsyzfnjxrcedigqlylkzfgjjqlnxgykozdkeufqzvmrptlbztdzzvapelruezcpculfyvvamqafmzmfiqqbmxrbmaystcxdkyksncpjovblcpttbjlvgiuqofutvdlfqslmlvkojebevlvpayfvnznkislnnvjivodfpcenkqwgfiosicdrvmgvijlayansgapidjrshuuwfsuxpzzdzvqvnjwjwfyavsohjuivhvqubsceyvzgeygagxfqbbilizokxplzybvutgmdbygfyyojgszbtsbadmqprjfrqivacvrnbneylryaamvhzojwvuemhjivcdytrhshtsjrfjtdvyioknshouwkrsuivkjngiocebvcwdcqepyimqeptunkmjdjdlpmckqqxpwugipqkveteomskrfeyujsqzqmnqzdgmjhpcqapwmxnhfgelvhlkohtzwxnknhkutxcmxolcbfujuhpzwqafkypwobgjqckndmpmelaptqtvbbggobhueecuniodhtfpaqsgacsntljzjbqahahzsseudlbiuedauoekxjwmcdfkptppmzjfebcggvxiqyttvmeilgdzbwkszxjdirbpwnpvukraiteobzlltdhnsqvmhjmalsyhaazflcvfxcyjtwebzlfncvpicwfhuwrowyxnepjcgagpqrraimszdnycqtedmbrgjicubcvfwiraxxryvarkxkqbrkknjqbowfihgizjuxttnaqxknhutbqmekpaaxsnjlgdfuoiatcdvvxsiedltftfmlcwvqiccifqazfemwbavhchgxcvbtpuurjclwpwoogvhmlrcgdmwhwrblbkekiyxojjqghefxxffoelfgvlawfqzyaniuwkmflgvpdvkciouzeysecliuhctwjohbesxzgiagkdncpfmjkmlutvayhwbnbvelxxddqkifgselscoyvkmjgyncytzcsihrilebtsrortwtsyggpsjpexlgvoeyemvsifxsgohtkebundjzatlzsmjsztapsbkvivfprkajh -->'
This has been happening for the past few weeks. It doesn't seem to matter whether I've recently done something else with Goodreads Sync or not.