For example:

emacs -Q /tmp/bar.cpp

Type:
C-x h C-M-\

First, note that std::variant is not indented with respect to std::pair.

Next, delete and re-insert the final angle bracket on the line that
reads:

    std::pair<ipfix::InfoElementID,std::vector<T>>,

Note the re-indention.

template <typename T>
using value_variant=3D
  std::pair<
  std::variant<
    ipfix::octetArray_t,
    ipfix::unsigned8_t,
    ipfix::unsigned16_t,
    ipfix::unsigned32_t,
    ipfix::unsigned64_t,
    ipfix::signed8_t,
    ipfix::signed16_t,
    ipfix::signed32_t,
    ipfix::signed64_t,
    ipfix::float32_t,
    ipfix::float64_t,
    ipfix::boolean_t,
    ipfix::macAddress_t,
    ipfix::string_t,
    ipfix::dateTimeSeconds_t,
    ipfix::dateTimeMilliseconds_t,
    ipfix::dateTimeMicroseconds_t,
    ipfix::dateTimeNanoseconds_t,
    ipfix::ipv4Address_t,
    ipfix::ipv6Address_t,
  std::pair<ipfix::InfoElementID,std::vector<T>>,
    std::pair<ipfix::TemplateID,std::vector<std::vector<T>>>,
    std::pair<std::vector<
                std::pair<
                  ipfix::TemplateID,
                  std::vector<std::vector<T>>>>>>,
  ipfix::length_t>;


Then, try C-x h C-M-\ again.  Note another reindentation.

template <typename T>
using value_variant=3D
  std::pair<
  std::variant<
    ipfix::octetArray_t,
    ipfix::unsigned8_t,
    ipfix::unsigned16_t,
    ipfix::unsigned32_t,
    ipfix::unsigned64_t,
    ipfix::signed8_t,
    ipfix::signed16_t,
    ipfix::signed32_t,
    ipfix::signed64_t,
    ipfix::float32_t,
    ipfix::float64_t,
    ipfix::boolean_t,
    ipfix::macAddress_t,
    ipfix::string_t,
    ipfix::dateTimeSeconds_t,
    ipfix::dateTimeMilliseconds_t,
    ipfix::dateTimeMicroseconds_t,
    ipfix::dateTimeNanoseconds_t,
    ipfix::ipv4Address_t,
    ipfix::ipv6Address_t,
    std::pair<ipfix::InfoElementID,std::vector<T>>,
  std::pair<ipfix::TemplateID,std::vector<std::vector<T>>>,
  std::pair<std::vector<
	      std::pair<
		ipfix::TemplateID,
		std::vector<std::vector<T>>>>>>,
  ipfix::length_t>;


Type C-x h C-M-\ again.  Another re-indentation.  This
one is stable, but incorrect.

template <typename T>
using value_variant=3D
  std::pair<
  std::variant<
  ipfix::octetArray_t,
    ipfix::unsigned8_t,
    ipfix::unsigned16_t,
    ipfix::unsigned32_t,
    ipfix::unsigned64_t,
    ipfix::signed8_t,
    ipfix::signed16_t,
    ipfix::signed32_t,
    ipfix::signed64_t,
    ipfix::float32_t,
    ipfix::float64_t,
    ipfix::boolean_t,
    ipfix::macAddress_t,
    ipfix::string_t,
    ipfix::dateTimeSeconds_t,
    ipfix::dateTimeMilliseconds_t,
    ipfix::dateTimeMicroseconds_t,
    ipfix::dateTimeNanoseconds_t,
    ipfix::ipv4Address_t,
    ipfix::ipv6Address_t,
    std::pair<ipfix::InfoElementID,std::vector<T>>,
    std::pair<ipfix::TemplateID,std::vector<std::vector<T>>>,
  std::pair<std::vector<
	      std::pair<
		ipfix::TemplateID,
		std::vector<std::vector<T>>>>>>,
  ipfix::length_t>;


Emacs  : GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo =
version 1.16.0)
 of 2023-04-14
Package: CC Mode 5.35.2 (C++//l)
Buffer Style: gnu
c-emacs-features: (pps-extended-state col-0-paren posix-char-classes gen-st=
ring-delim gen-comment-delim syntax-properties category-properties 1-bit)

current state:
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
(setq
 c-basic-offset 2
 c-comment-only-line-offset '(0 . 0)
 c-indent-comment-alist '((anchored-comment column . 0) (end-block space . =
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		   (c . c-lineup-C-comments)
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		    )
		   (brace-list-intro
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		    c-lineup-class-decl-init-+
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 adaptive-fill-regexp "[ 	]*\\(//+\\|\\**\\)[ 	]*\\([ 	]*\\([-=E2=80=93!|#%=
;>*=C2=B7=E2=80=A2=E2=80=A3=E2=81=83=E2=97=A6]+[ 	]*\\)*\\)"
 )

-- 
Michael Welsh Duggan
(md5i@md5i.com)