Something is wrong with the sequence of command blocks or the title command

I'm creating a map, and I want to make an effect that once the player gets into an area, there will be a title to tell the player the name of the area.

In the first command block, I used a repeating block that is always active:

title @a[r=150,tag=!mf] title §l§b梅恩费尔特港

following by an unconditional chain block that is always active:

title @a[r=150,tag=!mf] subtitle §l§bПорт. Менфальт

Then, I used a conditional chain block that is always active to give the player mf tag:

tag @a[r=150] add mf

Lastly I put a repeating block that is always active which coded:

tag @a[rm=151,tag=mf] remove mf

to remove the mf tag.

All those commands work well except the first two commands. It seems that the third block which gives the player mf tag always effect faster than the first two, whereas the whole command blocks are connected into a chain. During the test, I always get into this area with the mf tag and get out without the tag, but the titles are always absent.

Then, I stopped the execution of the third block by turning it into redstone-needed mode, finding the title works, but it splashes continually. So I have to find a way like this to let the title appears only once. However, I met this issue.

I would appreciate it if you reply me in early convenience.