Not seen this before and does not occur with files I have access to. Could you check in ArcGIS Pro. Can you indicate the source or provide a link to a similar file we can check out.
I don't have Pro, so will get that and see how it goes. The mosaic is a local 33Gb file, so not easily moved around. Most JP2 files load without issue, it's just a few that have been reprojected via ERDAS Imagine.
Why are you re-projecting as a pre-process? ArcGIS will re-project all imagery on-the-fly. Re-projecting data will only decrease the quality. If done on-the-fly you can control the resampling as appropriate. Similarly ArcGIS has a very large number of functions that can be applied on-the-fly enabling the imagery to be left in its original form and create a wide range of derivatives without requiring additional storage (and no pre-processing).
We are reprojecting to supply customers data in GDA2020. Not everyone is using ESRI so they need it reprojected. Also noticed that Arc does not appear to be registering the JPG2000 or ECW files as GDA2020/MGA50 (epsg:7850) for example. EPSG:7850 is recognised in ERMapper/QGIS as GDA2020, but Arc not picking this up. When the source properties are viewed, the Spatial Reference is <Undefined> and the XY Coordinate System is Unknown.
Not sure how they are defining the projection. It should be picked up. Suggest you use "Define Projection" too to set the projection to what it should be. As for the image that do not appear to display to full resolution. The text above indicates that these were re-projected first using Erdas. Do you have access the original images? Another thing you can do is run the data through optimize rasters.
Gave the Define Projection a go. If I set it to GDA94 Zone 50 it gives it a spatial reference. If I try GDA2020 Zone 50, the spatial reference is set to 'unknown'. Is GDA2020 a valid projection in ArcGIS 10.6 (version 10.6.0.8321) ?
You are going to need at least ArcMap 10.6.1 and the Coordinate System install as well as with the following blog article ArcGIS delivers GDA2020 NTv2 Grid files | Esri Australia Technical Blog Once installed you will be able to use the NTv2 grid files to do the reproject as well.
As Peter Recommends I would install ArcGIS Pro. The functionality here is far better than ArcMap and you will process the imagery quicker as you have access to more CPU and RAM to do the processing. Ensure you set the parallel processing factor to 95% as JP2's are memory and CPU intensive.