I had the problem once @George, and it was still on Mojave, in fact I think it was 2.4.5, and although I knew the fastest way around it was to download from your site and manually install, instead I went to ~/Library/Application\ Support/Wappler/temp/ and did an MD5 checksum on it, and downloaded off your site, and compared checksums.
The update version was different, I deleted it from ~/Library/Application\ Support/Wappler/temp/, used the menu to say check for updates, and all worked as per normal.
Well guess what just tried it on my other mac, and no go, also Mac Os X Mojave, will try give you as much info as possible so you can track the issue easier.
Environment variables:
Wappler 2.4.5 was open
I clicked in my Menu Bar and selected Check for Updates
A notification came up, I chose Download and Install
The filesizes and checksums are different, so not sure if there is a way for the update to check the checksum afterwards, and delete the file and re download if the file has been downloaded incorrectly.