Seems newly added a package which seems is separated from helm.el.

https://github.com/emacs-helm/helm-org

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On Sun, Aug 11, 2019 at 7:33 AM Nathan Neff <nathan.neff@gmail.com> wrote:

> I think I found the problem and have a fix!
>
> Long story short, I modified my helm-completing-read-handlers-alist
> and added an entry:
> (add-to-list 'helm-completing-read-handlers-alist
>     `(org-set-tags-command . helm-org-completing-read-tags)
> )
>
> I have all the gory details here:
> https://github.com/emacs-helm/helm/issues/2183
>
> Thanks all for your help, hope this helps someone else too :)
> --Nate
>
>
>
> On Sat, Aug 10, 2019 at 4:01 PM Nathan Neff <nathan.neff@gmail.com> wrote:
>
>>
>>
>> On Sat, Aug 10, 2019 at 3:44 PM Nathan Neff <nathan.neff@gmail.com>
>> wrote:
>>
>>> Hello all,
>>>
>>> I created a VM, installed Emacs 26.2 fresh, and installed various
>>> versions
>>> of org-mode using the tar.gz files from https://orgmode.org/
>>>
>>> I replaced org-mode in /usr/share/emacs/26.2/lisp/org with various older
>>> versions until I found the version of org-mode that breaks the helm tags
>>> completion.
>>>
>>> I found that the latest version of org where the feature works is
>>> Org-mode version 9.1.9.
>>>
>>
>> Oops - my aplogies - I assumed that the org-versions stopped at 9.1.9.  I
>> tested Org 9.1.14 which (to
>> my knowledge) is the last of the 9.1.X versions, and Org 9.1.14 works
>> correctly.
>>
>> I tested Org version 9.2 and Org version 9.2 is the version that breaks
>> the tags functionality
>> from Helm.
>>
>>
>>
>>> I will spelunk around in the code to see what might have changed the
>>> behavior - if anyone has
>>> suggestions or doesn't have this problem with an older version of org,
>>> please let me know - it could
>>> easily be something that I have set incorrectly.
>>>
>>> Thanks,
>>> --Nate
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Fri, Aug 9, 2019 at 4:28 PM Nathan Neff <nathan.neff@gmail.com>
>>> wrote:
>>>
>>>> Hello all,
>>>>
>>>> I'm hitting this problem with Org-mode 9.2.5:
>>>> https://groups.google.com/forum/#!topic/emacs-helm/tA6cn6TUdRY
>>>>
>>>> Problem synopsis:  When I use org-set-tags on a heading
>>>> with no tags, Helm gives me the correct prompt w/a list of all my tags.
>>>> After I have entered a single tag, then no more Helm suggestions are
>>>> offered.  This is the bug, and it was fixed at some point.
>>>>
>>>> Helm + org-mode *work correctly* when I run emacs using
>>>> the elpa/helm-20190726/emacs-helm.sh script which comes with Helm
>>>> for debugging purposes.  I notice that the org-version in the *working*
>>>> example
>>>> is 9.1.9 (which is, I presume) the stock org-mode that comes with Emacs.
>>>>
>>>> I have reproduced this problem on both Linux and OSX.
>>>>
>>>> Can anyone suggest a next step to take?
>>>>
>>>> Thanks,
>>>> --Nate
>>>>
>>>>