Premiere stops when changing sequence settign from HD to UHD

[heesu25317174nk5m]

I am experiencing problems when I try to change sequence setting from HD to UHD. 

I have upgraged Promiere Pro from 2019 to 2021 (Version 15.4.2 Build 3) and I have a Pemiere HD sequence with following sequence setting values:

-------------

Editing Mode : Custom

Timebase : 59.94 frames/ second

<Video>

  Frame size : 1920*1080

  Pixel Sequnce Pixels

  Fields : No fields 

  Display fromat : 59.95 fps drop-frame timecode

<Video preview> 

  Preview File Format : I-Frame Only MPEG

   Codec : MPEG Frame

   Width : 1920

    Height : 1080

------------

In the project window, I copied the HD sequence and changed the setting valuse to convert it into UHD sequence as below:

<Video>
  Frame Size : 3840 *2160

<Video Previews>

  Preview File Format : Quicktime

  Codec : Prores 422 LT

  Width : 3840

  Height : 2160

Other values are the same as HD sequence  

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The sequence has dosens of nested sequences included. So, I opened nested sequences by clicking mouse on them. Then, I changed the sequence setting values aa shown above. Not every time but very often when I changed the preview file format and codec of nested sequence to Quicktime and Prores 422LT 3840*2160, Premire Pro 2022 stops working and becomes out of response.  In the previous Premiere 2019, problems in this kind didn't occurred.

Original HD sequence's preview file format is I-Frame Only MPEG which doesn't provide 3840*2160 resolution, so I have to change it to Quicktime Prores 422 LT, 3840*2160. Problem frequently occures when this change is made. I have to restart Premiere Pro again and again every time Premiere becomes out of response. 

Do you know why this problem happens and how to fix it? Please help me out. 

[Ann Bens]

Dont change the resolution of the preview codec.

Keep it at 1920x1080. No need to make it the same as the sequence as you are not using the preview for export.

[heesu25317174nk5m]

Dear Ann, Thank you for your reply. The final delivery format is UHD. Along with the sequence setting change (including preview codec and resolution), I reconnect all video sources to UHD quality ones. So, UHD monitoring on a UHD precision monitor and UHD TV is essential. For me, chaning the preview file format, codec and resolution(3840*2160) is inevitble procedure. 

With Premiere Pro 2022, when changing preview file format, codec, and resolution of dosens of nested sequence on the timeline, some times Premiere Pro does not stop, but very frequently becomes out of response and I have to restart the Premiere Pro again and again which is time consuming and extemely annoying.  When previously working with Premiere Pro 2019, Changing preview file format, codec, and resolutionof nested sequnece to 3840*2160 didn't cause and problem at all. 

[Ann Bens]

You started out with i frame mpeg only which is a low quality preview codec anyways.

If you want good images set it to Prores HQ.