To clarify: I'm using a position+zoom effect with an image. On some of my clips, it follows the points (see video) just fine. However, on the next clip, it shows the red canvas box moving, but never actually moves the image itself.

It seems that on the second clip the first 3 keyframes worked and from the 4th it stops. Yes, please upload the project file here as attachment. Maybe you can upload the flag file as well.

Created attachment 118172 [details]
project file

project file attached.

Created attachment 118173 [details]
flag image

Here's the results of the XML file with the two panzoom filters (I immediately note that the filter ID on the first is "pan_zoom" but on the second it's "filter0")

<entry producer="28" in="0" out="79">
   <filter id="pan_zoom">
    <property name="background">colour:0x00000000</property>
    <property name="mlt_service">affine</property>
    <property name="kdenlive_id">pan_zoom</property>
    <property name="tag">affine</property>
    <property name="kdenlive_ix">1</property>
    <property name="kdenlive_info"/>
    <property name="disable"/>
    <property name="transition.geometry">0=-371/503:1920x1080:100;20=-735/347:1920x1080:100;29=-699/449:1920x1080:100;32=-732/399:1920x1080:100;43=-786/435:1920x1080:100;49=-651/487:1920x1080:100;58=-553/454:1920x1080:100;68=-462/491:1920x1080:100;79=-388/535:1920x1080:100</property>
    <property name="transition.distort">0</property>
   </filter>
  </entry>
  <entry producer="28" in="80" out="182">
   <filter id="filter0">
    <property name="background">colour:0x00000000</property>
    <property name="mlt_service">affine</property>
    <property name="kdenlive_id">pan_zoom</property>
    <property name="tag">affine</property>
    <property name="kdenlive_ix">1</property>
    <property name="kdenlive_info"/>
    <property name="disable"/>
    <property name="transition.geometry">0=-636/-291:1920x1080:100;5=-707/-270:1920x1080:100;10=-779/-262:1920x1080:100;15=-824/-275:1920x1080:100;19=-849/-279:1920x1080:100;24=-813/-279:1920x1080:100;31=-781/-261:1920x1080:100;37=-737/-226:1920x1080:100;44=-652/-136:1920x1080:100;54=-600/32:1920x1080:100;62=-573/160:1920x1080:100;72=-593/256:1920x1080:100;82=-597/357:1920x1080:100;88=-553/345:1920x1080:100;96=-495/370:1920x1080:100;102=-434/442:1920x1080:100</property>
    <property name="transition.distort">0</property>
   </filter>
  </entry>

I changed filterid to pan_zoom but it appeared to have no affect. For another helpful list, here's the data of the effects:

CLIP1:
 0=-371/503:1920x1080:100;
20=-735/347:1920x1080:100;
29=-699/449:1920x1080:100;
32=-732/399:1920x1080:100;
43=-786/435:1920x1080:100;
49=-651/487:1920x1080:100;
58=-553/454:1920x1080:100;
68=-462/491:1920x1080:100;
79=-388/535:1920x1080:100

CLIP2:
  0=-636/-291:1920x1080:100;
  5=-707/-270:1920x1080:100;
 10=-779/-262:1920x1080:100;
 15=-824/-275:1920x1080:100;
 19=-849/-279:1920x1080:100;
 24=-813/-279:1920x1080:100;
 31=-781/-261:1920x1080:100;
 37=-737/-226:1920x1080:100;
 44=-652/-136:1920x1080:100;
 54=-600/32:1920x1080:100;
 62=-573/160:1920x1080:100;
 72=-593/256:1920x1080:100;
 82=-597/357:1920x1080:100;
 88=-553/345:1920x1080:100;
 96=-495/370:1920x1080:100;
102=-434/442:1920x1080:100

I just noticed one more clue:

The second clip in the track view only shows four keyframes (even though the red lines and dots in the preview show many more). But even then, it doesn't seem to track those dots four keyframes.

Found a workable solution!

For each affected clip:

 - Copy the clip, paste the clip (it will STILL be broken) to somewhere (another channel, or beside it).

 - Click the new clip. (referred to as clip2 from now on)

 - Delete all effects from clip2.

 - Copy (control-C) the original clip again.

 - Right-click on clip2 and select "paste effects"

The keyframes work now!

Thank God.

Using Windows latest: 18.12.1

If helpful, I may be able to do the exact steps before and after for each step, into a saved projected file to show the internal XML steps breaking.

Since then, Kdenlive 19.x and 20.x releases got much more stable.