Using older versions
The ElectrumSV developers only support the latest officially released version and do not provide support for older versions. You can continue to use older versions without our support, but they may stop working unless you are willing to invest a lot of time and effort. Do not contact us about this. We are more than willing to offer support if you upgrade to the latest officially released version and observe the same problems there.
You need a server
Versions of ElectrumSV before 1.4.0 use an open source server project called ElectrumX. Most users do not even pay much attention to the fact that generous community members and businesses run these servers for them to use for free. While a blockchain is small and rarely used, this was feasible. But as blocks get larger and larger, it will become impractical and expensive for people to casually run these servers.
No-one will be running these ElectrumX servers and your wallet will not be able to:
Detect any incoming or outgoing payments.
Broadcast any transactions.
Do pretty much anything other than work as if it were offline.
If you want the wallet to work you will need to run your own ElectrumX server, or pay someone else to run the server for you. This will require additional programming work to deal with all the indexing needs and the indexed blockchain data, as the blocks get bigger and bigger and the blockchain data accrues.
Your responsibility
If you do not upgrade to the latest version of ElectrumSV, then you are responsible for any problems you have. You are responsible for the time, effort and costs in running the required servers when the existing ones finally go down.