Dropbox wont replicate encrypted files

I hope someone out there can help me with this problem as it’s driving me mad….I’ve tried everything, deleting Dropbox, re-installing it, checking the sign-in details  on bothall my laptops, and spending literally hours in the forums etc all to no avail.

I have two laptops. Both use the same Dropbox account and version of the software – 98.4.158

#1 has Windows 10 Home Edition Build 18363.836 installed, and #2 was an older laptop again with Windows 10 Home Edition as above. It has been replaced by a brand new laptop with Windows 10 Professional Build 19041.264 in the vain hope that a brand spanking new installation would cure my problem – no such luck.

If I try a small file (Word doc - 20Kb) both work fine and show the changes made by and on each other. If I try a larger file (Excel 90Kb) then again all works well. So all of my dinky little files seem ok.

However I also have 9 larger files starting at 1Mb up to 128Mb. These do not work. They all have the same file extension (.locker) and are all encrypted by the Truecrypt executable.  These need to be encrypted as they contain personal data. At this point it’s worth noting that the replication of encrypted files on both laptops worked fine up until about 7 months ago.

I thought maybe the extension might have been the problem so I changed one file extension from .locker to .lkr. Dropbox recognised this and the also the subsequent rename back to .locker again. Not that then.

If I decrypt and change the contents of the smallest file (1Mb) then re-encrypt it, then the Dropbox cloud does not see a change, only the local copy – on either laptop. It knows the file has been accessed but not changed. If I repeat the above using Veracrypt – it’s the same again.

So on the face of it, it seems the problem is due to the file being encrypted preventing replication. Has anyone else had the same problem and if so, how did you solve it ? and it’s not encryption then please help me how to fix the problem. Thanks.