Chain Split

According to information from the site on Tuesday 1 August 2017 at 03:00 GMT, the Bitcoin network may be subject to bifurcation and remain unstable for an unknown period of time. This means that any Bitcoins that you receive after time may later disappear from your wallet or will not be accepted as payment by other users.
This can happen if SegWit is not activated according to BIP141 or SegWit2X, which can lead to network separation, which will create two competing blockchains. To be precise, the potential threat is the activation of the so-called UASF (BIP148), which is not mentioned in the publication.
Remember that you are responsible for the safety of your bitcoins, and if you lose control over them for any reason — this will be your personal loss.
If you accept payments in bitcoins, we recommend that you stop this at least 12 hours before the above date (August 1, 03:00 GMT), although it’s better to do it in 48 hours — it will be safer. This will give time to confirm all pending payments in the Bitcoin battle unit before activating SegWit.
If you send bitcoins as payments, note that many services may stop accepting them at this time or a little earlier.
Be careful when storing your bitcoins on an exchange or other services that don’t allow you to create a local backup of your private keys. If they accept transactions during these events, they can lose money and are likely to transfer losses to their users. In case, in the end, two or more competing blockchains appear, they may refuse to provide you with your bitcoins in versions that they do not like.
Bitcoin may experience significant price fluctuations in relation to other currencies. Learn more about price volatility and make sure that you do not keep the bitcoins worth more than you can afford to lose.

During the events

Do not trust any payments that you receive after August 1, until the situation clears up. Regardless of how many confirmations received a new payment, it can disappear from your wallet.
Try not to send payments. During the event, there may be two or more competing blockchains, and you can send a payment that will enrich the recipient at your expense.
Beware of proposals that allow you to invest in “bifurcated” coins. Some of these suggestions may be fraudulent, and software that requires you to share your coins can steal them.