You want to confirm that the foreign entity is properly classified as a partnership. Foreign limited liability companies default to be classified as corporations. Foreign limited liability companies are only treated as partnerships for US tax purposes if a Form 88332 has been filed.
A UK LLP is not a partnership, so Forms 926 and 5471 would be prepared - not Form 8865. CFC, SubPart F, GILTI and PFIC rules may all need to be addressed - along with getting the reporting refigured using US GAAP.
PS – Greeting from London, England. Grey and rainy ...